METHOD FOR SELECTING A WIRELESS SERVICES PROVIDER IN AN ENVIRONMENT OF MULTIPLE SERVICE PROVIDERS USING A GEOGRAPHICAL DATABASE BACKGROUND OF THE INVENTION Field of the invention The present invention relates to communications; more specifically to communications to an environment of multiple service providers. Description of the Related Art Figure 1 illustrates a portion of the radiofrequency spectrum. The central frequency range around 800 MHz has historically been known as the cellular frequency range and the frequency range centered at around 1900 MHz, is a more recent defined frequency range associated with personal communications services (PCS) . Each frequency range, ie the cellular and PCS, are broken down into two parts. In the cellular frequency range 10, there is the uplink portion 144, which is used for communications from a mobile communication device to a base station such as a cellular base station. Portion 16 of the cellular frequency range 10 is used for downlink communications, that is, communications from a cellular base station to a mobile communication device. Similarly, the
REF: 23437 portion 18 of the PCS 12 frequency range is used for uplink communications, that is communications from a mobile communications device to a base station. Portion 20 of the PCS frequency range 12 is used for downlink communications, i.e. communications from a base station to a mobile communications device. Each of the frequency ranges is broken down into bands that are typically associated with different service providers. In the case of a cellular frequency range 10, frequency bands 30 and 32 are designated as "a" band for uplink and downlink communications respectively. In a particular geographic area, a cellular service provider is assigned to the frequency band "a" in order to carry out mobile communications. Similarly, in the same geographical area another cellular service provider is assigned frequency bands 34 (uplink) and 36 (downlink) that are designated band "b". The frequency spectra assigned to the service providers are separated so as not to interfere with the communications between them and thus allow two separate service providers to provide service in the same geographical area. Recently, the Government of the United States. put the PCS frequency spectrum on sale to service providers. As with the cellular frequency range, the PCS frequency range is broken down into several bands, where a different service provider can use a particular frequency band for which it is licensed within a particular geographical area. PCS bands are referred to as A, B, C, D, E, and F. Band A includes uplink band 50 and downlink band 52. Band B includes uplink band 54 and band Downlink 56. Band C includes uplink band 58 and downlink band 60. Each uplink and downlink band of bands A, B, and C has an approximate width of 30 MHz. band D includes uplink band 62 and downlink band 64. Band E includes uplink band 66 and downlink band 68. Likewise, band F includes uplink band 70 and bandwidth downlink 72. The uplink and downlink bands of bands D, E and F are approximately 10 MHz wide each. It should be noted that with the cellular and PCS frequency bands, it is possible to have as many as 8 different wireless communication service providers in a particular area. Each of the different cellular and PCS bands consists of control channels and communication channels in both the uplink and downlink direction. In the case of analog cellular bands, there are 21 control channels for both "a" and "b" bands. Each of the control channels includes an uplink and downlink portion. The control channels transmit information such as SOC (system operator code), a SID (system identifier code), information for call configuration with location information and other general information, such as information relating to registration with the system. mobile communication The portion of the cellular band spectrum not occupied by the control channels is used for communication channels. The communication channels transport voice or data communications, wherein each channel consists of an uplink and downlink communications link. Currently there are several cellular communications standards. A known analog standard EIA / TIA 553 builds on the AMPS standard (advanced mobile telephony services). This standard supports 21 analog control channels (ACC) and several hundred analog voice or traffic channels (ACC). A new standard is the EIA / TIA IS54B standard that supports dual mode operation. The operation in dual mode refers to having an analog control channel and either an analog voice / traffic channel or a digital traffic channel (DTC). The AVCs or DTCs are used for current communications and the ACC is used to transfer information relating to, for example, call configurations, service provider identification and other general or system information. A new standard is the EIA / TIA IS1366 standard that supports communications covered by both dual and analog modems and also includes a fully digital communications scheme that is designed for the PCS AF frequency bands and the "a" cellular frequency bands and "b". This standard allows a digital traffic channel (DTC) and a digital control channel (DL). In the case of DTC, not only voice or data are communicated, but also, a digital channel locator is transmitted in the DTC. The DL allows a mobile communications device that locks into the DTC to use the information in the DL to locate a DCCH for purposes of obtaining information such as SOC, SID, location information and other general information of the system transported in the channel. digital control When a mobile communication device such as a mobile phone attempts to register with the service provider, it locks onto a control channel and reads information such as SOC and SID. If the SOC and / or SID correspond to a service provider with which the user has a communication services agreement, the telephone can register with the service provider's mobile communications system through an uplink control channel.
Figure 2 illustrates a map of the U.S.A. It shows cities such as Seattle, Chicago and Washington, DC. For example, in Seattle, frequency band A has been licensed to SOC (service operator code) 001 with a SID 43 and band C has been licensed to SOC 003 with a SID 37. In Chicago, assume that the band frequency C has been licensed to SOC 001 with a SID equal to 57, and that band B has been licensed to SOC 003 with a SID 51. In Washington DC, assume that the frequency band "a" has been licensed to SOC 001 with a SID 21 and that band A has been licensed to SOC 003 with a SID 17. It should be noted that the same SOC can be found in several different sites although in different frequency bands. It should also be noted that the same SOC will be associated with different SIDs in each geographical area and that in the same geographical area different service providers have different SIDs. If a particular subscriber to a wireless telecommunications service has an agreement with a service provider that has a SOC of 001, that subscriber will prefer to use the system with a SOC of 001 because the subscriber will likely receive a less expensive fee. When the subscriber is in Seattle, he would prefer to be in band A, and if he is in Chicago in band C, and if he is in Washington DC, in band "a". The situation actually described presents a problem for a wireless communications service subscriber. As a subscriber moves from one area of a country to another, when the phone is turned on, it looks for the "home" service provider or the service provider with which the subscriber has a pre-established agreement. If, for example, the subscriber travels from Seattle to Chicago, when he turns on the phone in Chicago, the phone will search through the different bands of the spectrum to identify the service operator with the code 001 in order to find the desired service provider. In order to find a particular service provider, the phone may have to search both through both "a" and "b" cell bands as well as through the eight PCS bands. It should be remembered that there are up to 21 different ACCs in each of the cell bands "a" and "b". It may be necessary to verify 42 ACCs in order to find an ACC from which a SOC or SID can be obtained. Additionally, the search for a particular SOC or SID in PCS bands A to F is particularly time consuming. The digital control channels (DCCHs) that contain the SOC and SID are not assigned to specific frequencies within a particular PCS band. As a result, the mobile communications device may find it necessary to search through the spectrum of each PCS band looking for a DCCH or an active DTC having a digital channel locator (DL), which will direct the mobile communication device to the DCCH. As illustrated above, the process of searching for a particular service provider is laborious and may require a period of time in the order of several minutes. SUMMARY OF THE INVENTION One embodiment of the present invention provides a method for locating a particular or convenient communications service provider in an environment having a plurality of service providers. After switching on, a mobile communications device such as a cell phone checks the most recently used control channel to determine if an optimal service provider is available in that channel. If an optimal service provider is not available or if that channel is not available, the mobile communications device performs a search through the frequency spectrum in a predetermined order until an optimal or acceptable service provider is located. In another embodiment of the invention, the frequency spectrum is searched in a predetermined order that changes based on the information provided by a mobile communications device distributor or mobile device user. Still in another embodiment of the invention, the default order to search the spectrum for service providers is updated by air programming. In yet another embodiment of the present invention, the predetermined order to search is based on the operational history of the mobile communications device. In yet another embodiment of the present invention, the communications device tunes to a first frequency band and receives a geographical identifier from the service provider operating in the first frequency band. The received geographic identifier is compared with a list of stored geographic identifiers, in order to try to locate a corresponding stored geographic identifier. Each of the stored geographic identifiers is associated with a convenient frequency band that has a convenient service provider. If, when comparing the received geographical identifier with the corresponding stored geographical identifier, no correspondence occurs, the frequency bands are examined until a second frequency band having a convenient service provider is located. The list of stored geographic identifiers is then updated, so that the second frequency band is associated with the received geographical identifier. Brief Description of the Dibules Figure 1 illustrates the frequency spectrum used for wireless communications; Figure 2 illustrates service areas within the U.S.A .;
Figure 3 is a block diagram of a mobile communication device; Figure 4 is a flow diagram illustrating a spectrum search routine; Figure 5 is a flow diagram illustrating the global spectrum search routine; Figure 6 is a flow diagram illustrating a periodic search routine; Figure 7 is a flow diagram illustrating a routine for searching for received signal strength; Figure 8 illustrates a search program; Figure 9 illustrates a list organized by priority of service providers; and Figure 10 illustrates a list of geographic identifiers and convenient frequency bands ordered by priority. Detailed Description of the Invention Figure 3 illustrates a block diagram of a mobile communication device such as a cell phone or personal communication device. The mobile communications device 10 includes transceiver 12 that sends and receives signals from the antenna 14. The mobile communications device 10 is controlled by the control system 14, which may include a microprocessor or a microcomputer. The control system 14 uses the memory 16, to store programs that run and to store information that is supplied by the user, the distributor, the communications service provider or the manufacturer. Information such as user preferences, user telephone numbers, preferred service providers and frequency search programs are stored in memory 16. Memory 16 may include storage devices such as random access memory (RAM), memory read only (ROM) and / or programmable read only memory (PROM). A user communicates with the control system 14 by the keyboard 18. The control system 14 communicates information to the user through the display 20. The display 20 can be used to display information such as status information and items such as telephone numbers powered by the numeric keypad 18. Sound information to be transmitted from the mobile communications device 10 is received by the microphone 22 and sound communications received by the mobile communication device 10 are reproduced to the user by the speaker 24. After initially energizing , a mobile communications device locates a service provider and registers with the service provider. With reference to Figure 1, service providers are located in a plurality of frequency bands across the radio spectrum. In order to find a service provider, the communications device looks for the spectrum to find the service providers. The communications device examines the received service provider code, for example the SOCs (service operator code) or SIDs (system identification code) to determine whether the service provider is an optimal, preferred or prohibited service provider . Figure 4 illustrates a process or program that executes the control system 14 in order to find a convenient service provider. After energization, step 30 is executed to initialize a non-optimal flag by releasing the flag. Step 32 determines whether the last service provider, that is, the service provider used before shutting down, was an optimal service provider. This is determined by checking the SOC or SID of the last service provider and determining whether the SOC or SID of that service provider corresponds to SOC or SID of an optimal service provider. The SOC or SID of the last service provider and a list of optimal and preferred service providers are stored in memory 16. If in step 32, it is determined that the previous service provider was not optimal, a search of global spectrum. If the last service provider was optimal, step 34 is executed where the system 14 attempts to lock into the control signal of the service provider. If the interlock does not succeed, which may indicate that the control channel is no longer available or out of range, the global spectrum search is executed. If the interlock is successful, step 36 is executed. In step 36, it is determined whether the control channel contains the SOC or SID of an optimal service provider. Again, this is determined by comparing the SOC or SID of the control signal with a list of optimal service providers SOCs or SIDs. If the SOC or SID does not belong to that of optimal service providers, the search for the global spectrum 33 is executed and the identity of the frequency band in which the non-optimal SOC or SID is located, is passed to the search routine global 33, to avoid unnecessary search of this portion of the spectrum, again. If in step 36, it is determined that an optimal service provider has been located, step 38 registers the communications device 10 with the service provider. Step 40 is a quiescent state wherein the control system 14 simply verifies the control channel of the service provider for general information of the communication system and for location information that may indicate an incoming communication. While in the idle state 40 a synchronizer is activated that allows a low service cycle search to be performed if the telephone is currently registered in a non-optimal service provider system. This situation may arise if the search for global spectrum 33 provides a preferred but not optimal service provider. Periodically, as every 5 minutes the step 42 is executed to determine if the non-optimal flag has been placed, if the non-optimal flag has not been placed, the control system 14 returns to the rest stage 40. If it has been placed the non-optimal flag, step 42 leads to execution of the periodic search routine 44, where a search is performed in order to try to locate an optimal service provider. If the optimal search routine 44 produces an optimal service provider, the non-optimal service provider flag is released and the mobile communications device registers with the optimal service providers, while executing the periodic search routine 44. The device of mobile communications then enters a state at rest upon executing step 40. If an optimal service provider is not located in routine 44, control system 14 returns to a state at rest upon executing step 40. Figure 5 illustrates a flow chart of the global spectrum search routine 33, which is executed by the control system 14. In step 60, it is determined whether the last control channel used by the mobile communication device was a control channel related to personal communication services, that is, a control channel in bands A to F. If the last control channel was not a PCS control channel, step 62 is executed In step 62, it is determined whether the mobile communications device can latch on, or receive and decode the last ACC (analog control channel) that was used. If the mobile communication device can successfully latch on the last ACC, step 64 is executed. If the communication device can not latch on the last ACC, step 66 is executed. In step 66, an RSS (received signal strength scan) is performed. This stage involves the tuning of the mobile communication device to each of the 21 ACCs associated with the cellular band of the last used ACC, and attempts to lock into the strongest received signal. In step 68, it is determined whether an interlock has been achieved. In step 68 if an interlock is not obtained, a predetermined search program is executed in order to find a service provider; if in step 72, an interlock is obtained, step 64 is executed where the SOC or SID obtained from the control channel is compared to a list of optimal SOCs or SIDs. In step 70, if the received SOC or SID is associated with an optimal service provider, step 72 is executed where the mobile communications device releases the non-optimal flags, registers with the communications service provider and then enters into a state at rest when executing step 40 of Figure 4. If in step 70 it is determined that an optimal SOC or SID service provider is not received, step 74 is executed, where the identity of the frequency band is newly searched is stored in memory 16. Step 78 is executed after step 74, after 68 if an interlock is not obtained, or after step 60 if the last control signal was from a PCS frequency band. In step 78, a search program is downloaded using a master search program. When the search program is downloaded in step 80, the previously searched frequency bands are removed from the downloaded program in order to avoid search bands that have already been searched. For example, the bands searched in the search routine discussed with respect to Figure 4 and the cell band search discussed with respect to step 70 are removed from the search program. After the modified search program has been loaded, a search pointer is initialized to mark the first band identified by the modified search program. The first band identified in the modified program is searched for with respect to the received signal strength (RSS) of the routine of step 79. In the case of bands "a" and "b", the ACC is chosen with the signal stronger. In the case of the PCS bands, this is bands A to F, 2.5 MHz sections of each band are looked for in stages of 30 Kilohertz. The mobile communications device tunes the strongest signal that crosses a minimum threshold, for example -100 dBm, within the 2.5 MHz band examined. In step 80, it is determined if the signal is valid as it is, it adapts to one of the aforementioned standards. If it is not valid, the search pointer is incremented in step 96, and if the signal is valid, step 82 is executed. In step 82, it is determined whether the signal is an ACC. If the signal is an ACC, the SOC or SID is decoded in step 90. If the signal is not an ACC, step 84 determines whether the received signal is a digital traffic channel (DTC) or a digital control channel ( DCCH). If the signal is a DCCH, the SOC or SID is extracted in step 90. If it is determined that the received signal is a DTC, step 86 is executed where the DL (digital channel locator) is extracted to identify the location of the DCCHs associated with the DTC that has been received. In step 88, the mobile communication device tunes to the strongest DCCH of the digital control channels identified by DL. In step 90, the SOC or SID of the received DCCH is extracted and in step 90, it is determined whether the SOC or SID is associated with an optimal service provider. If the SOC or SID is associated with an optimal service provider, step 92 releases the non-optimal flag and stage 96 registers the mobile communications device with the service provider. After step 96, the communication device enters the idle state in step 440 of FIG. 4. If in step 92, it is determined that the SOC or SID does not belong to that of an optimal service provider, it is executed step 94 wherein SOC or SID is stored in memory 16, indicating whether the SOC or SID was at least a preferred one instead of an unwanted or prohibited service provider with the spectral location of the control channel of the SOC or SID. In step 96, the search pointer identifying the band to be searched is advanced to identify the next band in the search program. In step 98, it is determined whether the pointer has reached the end of the search program. If the end of the search program has not been reached, step 92 is executed to perform another received signal strength search routine as discussed above, and if the last frequency band has been searched, step 100 is executed. In step 100, the mobile communication device registers. with the best stored SOC or SID, this is a SOC or SID that has at least been associated with a preferred service provider. The best service provider can be identified by comparing the SOCs or SIDs with a list of preferred SOCs or SIDs. The list of preferred SOCs or SIDs can include the optimal SOCs or SIDs and a prioritized priority list of preferred SOCs or SIDs, where the higher priority will obtain preference for registration. The list also includes SOC (s) or undesirable or prohibited SID (s) that are used only in emergencies (for example, 911 calls) or if the user enters a replacement command. After registering with the service provider in step 100, step 102 is executed to adjust the non-optimal flag, and then step 440 of Figure 44 is executed where the mobile communications device enters the idle state. It should be noted that the search operation of Figures 4 and 5 can be carried out in a simplified manner. With respect to Figure 4, control system 14 can execute step 33 after step 30 while steps 32, 34, 36 and 38 always skip. With respect to Figure 5, control system 144 can initiate the search for global spectrum with step 78 while always skipping steps 60 to 74. Figure 6 illustrates a flowchart for the periodic search routine executed by the control system 14. In step 120, it is determined whether has placed the periodic search flag. If the periodic search flag has not been placed, step 12 is executed where the periodic search flag is placed and the search program is initialized by loading the master search program in the search program used by the search routine periodic; however, the frequency band currently received is not included in the search program used for the periodic search routine. Step 122 also adjusts a search pointer A to the first band in the search program. In step 122, a received signal intensity (RSS) search routine is performed. As in step 79, of the global spectrum search routine of Figure 5, step 124 is an RSS routine of any PCS and cellular bands that are in the search program. In the case of a cellular band search, the 21 ACCs are searched using a search of ripped signal strength, ie the transceiver is tuned to the strongest ACC. In the case of a PCS frequency band search, as previously discussed, each band is decomposed into segments of approximately 2.5 MHz where a search of each segment is performed in the 30 kilohertz stage. The signal within the 2.5 MHz segment and over a minimum threshold, such as -100 dBm, is chosen. In step 126, the selected signal is examined to determine if it is valid by conforming to one of the previously referenced standards. If the signal is invalid, step 144 is executed and if the signal is valid, step 129 is axis-cuta. Step 129 determines whether the signal is an ACC. If the signal is an ACC, step 130 is executed when the SOC or SID is extracted and if the signal is not an ACC, step 132 is executed. Step 132 determines whether a DTC signal was received. If the signal is not a DTC signal (therefore it is DCCH signal) step 130 is executed to extract the SOC or SID from the DCCH signal. If in step 132 it is determined that a DCCH has been received, step 134 is executed to extract the DL to allow tuning to a DCCH. In step 136, a signal strength search is received from the DCCHs, where the strongest signal is chosen, and then step 130 is executed to extract a SOC or SID from the signal. In step 138, it is determined whether the SOC or SID is an optimal SOC or SID. If the SOC or SID is optimal, step 140 releases the non-optimal flag and in step 142, the mobile communications device registers with the service provider associated with the optimal SOC or SID. Step 140 of Figure 4 is then executed to enter the idle state. If in step 138 it is determined that the SOC or SID was not an optimal service provider, step 144 is executed. In step 144, the search pointer is incremented to the next band to be searched. In step 146 it is determined that the entire search program has been completed. If the program has not been completed, step 140 is executed in such a way that the mobile communications device can be returned to the idle state. If in step 146, it is determined that the search program has been completed, step 146 releases the periodic search flag and then step 40 is executed in such a manner that the mobile communications device can enter the idle state. Figure 7 illustrates a flow diagram of the RSS routine or received signal intensity search routine that was carried out, for example in steps 79 of Figure 5 and 124 of Figure 6. Step 170 determines whether the The band you are looking for is one of the "a" or "b" cell bands. If a cellular band is searched, the stage 172 is executed, where the 21 ACCs are searched to determine which is the strongest, the strongest ACC is tuned by the transceiver 12 under the control system 14 and then leaves the RSS routine. If in step 170 it is determined that a cellular band is not searched, step 178 tunes the transceiver 12 to the start of the first 2.5 MHz band in the PCS band sought. Step 178 also releases a search eraser memory location in memory 16. The eraser eraser is used to record the amplitude or strength and location of a received signal. In step 180, it is determined whether the signal that is received is greater than a threshold. If the signal is greater than the threshold, step 182 is executed, if the signal is greater than the threshold, step 184 is executed. In step 182, it is determined whether the strength of the received signal is greater than the signal strength value stored in the eraser. If the received signal is not greater, then step 184 is executed. If the received signal strength is greater, step 186 is executed and the current signal strength is recorded in the search draft with the signal search received in the spectrum. In step 184, the transceiver 12 is tuned to a frequency of 30 kilohertz greater than the frequency at which it was tuned. Step 188 determines whether the new frequency extends beyond the 2.5 MHz band currently being sought. If the new frequency does not exceed the 2.5 MHz band, step 180 is executed to again examine the received signal strength with respect to the signal strength or amplitude value stored in the search eraser. If in step 188 it is determined that the 30 kilohertz increase extends beyond the 2.5 MHz band examined, step 190 is executed. In step 190, the transceiver tunes to the signal location specified in the search draft . If the signal is a valid signal and can be decoded, the RSS routine is exited. If the signal is not valid or can not be decoded (for example the signal does not conform to the aforementioned standards), step 192 is executed. In step 192 the transceiver is tuned to the start of the next 2.5 MHz band within the PCS band searched. Step 194 determines whether the new 2.5 MHz band extends beyond the currently searched PCS band. If the new increment extends beyond the searched PCS band, it exits the periodic search routine. If the 2.5 MHz increase does not result in extending beyond the searched PCS band, step 196 is executed. In step 196, the search draft containing signal strength measurements and signal location information is released to prepare search in another band. After step 196, step 180 is executed as described above. Figure 8 illustrates a master search program. The master program is used to initialize search programs used in the search routines described above. The master search program is stored in a memory such as the memory 16. The master search program can be initially programmed by the manufacturer, distributor or user of the mobile communication device. It will be noted that the first location in the search program is left unprogrammed. If left blank, the target is ignored when the search programs for the search routine are initialized. It is convenient to program the first location with the band in which the user's local service provider resides. For example, if the user has a service agreement with a licensed service provider to operate in the B PCS band within the SID or geographical area in which the user is most frequently located, the B band is programmed in the first slot of the master search program. For example, if band B is programmed in the first slot, the slot originally containing band B becomes blank. This avoids searching the same band twice, it will also be noted that the user can vary the master search program through the numeric keypad 18. Additionally, the master search program can be reprogrammed using signals received over the wireless communication channel. For example, the mobile communications device may be restricted to accept new programming for the master search program only from a service provider that transmits local SID and an optimal SOC. It is also possible to accept the air programming if the service provider sends a pre-arranged code. It is convenient to restrict the programming in the air through the use of local SID codes and / or optimal SOCs., to avoid accidental or undesirable alteration of the master search program. On-air programming can be implemented using for example logical sub-channels of a digital control channel. Loe eub-canalee logicoe have the ability to transmit data routed to a particular mobile communications device and to receive data as a confirmation data of the mobile communication die. When the search programs are initialized using the master search programs, it is also possible to precede the first location in the master search program with other frequency bands based for example on the previous history of the use of the mobile communication devices. For example, the first location searched may be the location where the phone was turned off (de-energized) or the location where the phone was last turned on (energized). Figure 9 illustrates a table stored in memory 16 that defines the SOC and the SID of optimal service providers, and the SOCs and SIDs of preferred service providers. The SOC or SID with the lowest number has the highest priority and is preferred over service providers with higher numbers and therefore a lower priority. For example, a SOC or SID with a level of priority 2, would be preferred over a SOC or a SID with a priority level of 5. The table can also include SOCs or SIDs that are indeeeable or prohibited. In the case of SOCe or SIDe which is prohibited, it is convenient to allow connection to the prohibited SOCs and SIDs, when an emergency call such as a 911 call is attempted or when the user enters a replacement command. The table in Figure 9 can be programmed by the manufacturer, by the distributor when the phone is purchased or by the ueuario. It is also possible to program the table of Figure 9 in the air, using restrictions similar to those used when organizing the master air search program. Figure 10 illustrates a grid of geographic identifiers with associated frequency bands, which are organized by priority based on the convenience of the service provider operating in the band. The screen of Figure 10 is stored in memory 16 and is used for the selection of a frequency band containing a convenient service provider. After initial energization, the communications device 10 tunes to the first frequency band of the frequency search program, the last frequency band used or the frequency band used when the device was last energized. After tuning to the band, the communications device verifies the control signal associated with the band to obtain a geographical identifier such as a SID. The communications device then accesses the table in Figure 10, in order to determine which frequency band has a convenient service provider. For example, if the device receives a geographical identifier such as 51, the table in Figure 10 instructs the communication die to be tuned to the frequency band C for the most convenient service provider. The communications device then tunes to frequency band C and attempts to register with the service provider operating in frequency band C. If for some reason the device is not successful in registering with the service provider in the frequency band. C, the next highest priority frequency band can be used. In the case of SID 51, the next most convenient frequency band is the "b" cell band. Again, the communication device will tune the frequency specified by the table and attempt to register with the service provider operating in that frequency band. The table in Figure 10 gives the frequency bands in an order organized by priority. The frequency bands listed at the far left are the best or most convenient frequency bands, that is, the frequency bands with the best or most convenient service provider. The frequency bands listed further to the right decrease in convenience or priority until the prohibited frequency bands are listed on the far right. The banned frequency bands can be used in emergency situations or when they are overcome by the operator of the communications device. The table of Figure 10 can be programmed in memory 16 of the communication device by the manufacturer of the device, by the distributor, or by the user by means of the numeric keypad. It is also possible to program the table of Figure 10 using on-air programming in a manner similar to that used to organize the search program of Figure 8 or the table of service providers organized by priority of Figure 9. In some cases, there can not be a geographical identifier or SID in the table of Figure 10 for an identifier that is received from a control channel to which the communication pattern is tuned. In this case, the communications device executes the search algorithms discussed previously, in an effort to locate a convenient service provider. When a convenient service provider has been located, the table in Figure 10 is updated to list the previously unlisted geographic identifier and the frequency at which the convenient service provider is located. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, which is clear from the present description of the invention. Having described the invention as above, the content of the following is claimed as property: