METHOD AND APPARATUS FOR RECEIVING COMMUNICATION SIGNALS Field of the Invention The present invention relates generally to communication devices, and more particularly, to a method and apparatus for receiving communication signals. BACKGROUND OF THE INVENTION With the increasing use of wireless communication devices, the spectrum has become insufficient. In many cases, network operators that provide services over a particular band have had to provide services over a separate band to accommodate their clients. For example, network operators that provide services over a GSM system in a frequency band of 900 MHz have had to depend on a DCS system at a frequency band of 1800 MHz. Accordingly, the communication, such as cellular radiotelephones, must be able to communicate on both frequencies, or even a third system, such as PCS 1900. Such a requirement to operate at two or more frequencies creates a number of problems. For example, the communication device would have an increased size and cost if the receiver included separate components to receive signals in each band. According to the above, there is a need for a method and apparatus for receiving communication signals in a plurality of bands while minimizing the increase of components. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a block diagram of a communication device according to the present invention; Figure 2 is a block diagram of the receiver 127 of Figure 1 according to the present invention; Figure 3 is a schematic diagram of a mixer 234 according to the present invention; Figure 4 is a block diagram of the receiver 127 of Figure 1 according to an alternative embodiment of the present invention; and Figure 5 is a schematic diagrame of a mixer 234 according to an alternate embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION A method and apparatus allow a communication device to operate in multiple bands, such as bands of GSM 900 MHz, DCS 1800 MHz, and PCS 1900 MHz by eliminating the need for a mixer for each band. In a dual band GSM / DCS 1800 radiotelephone, for example, the local oscillator (LO) injection frequencies for both GSM and DCS bands are provided to a mixer through the use of combination filters. In this way, the requirements for duplex transmission and coupling with the mixer input are simplified and signal losses are minimized. The RX / LO combination filters, one for each GSM and DCS band, are designed with RX and LO input ports and a common RX / LO output port. The common output ports of the GSM RX / LO combination filter and the DCS RX / LO combination filter are duplexed to the mixer input. Due to the duplex transmission requirements between the RX and LO injection, the frequencies are accommodated by the combination filters, the circuit design reduces the number of duplex lines to the mixer from six to two for a communication device. double band and from ten to four for a triple band communication device. Also, the input impedance coupling of the mixer is designed to couple the impedance for the signals received in each band, as well as providing an RF shunt on the IF frequency. Finally, the output circuit of the mixer provides a low impedance at the RF input frequency and also a coupling with the input of the IF filter. Turning now to Figure 1, a block diagram of a wireless communication device such as a cellular radiotelephone incorporating the present invention is shown. In the preferred embodiment, an ASIC 101 configuration generator, such as a CMOS ASIC available from Motorola, Inc. and a microprocessor 103, such as a 68HC11 microprocessor also available from Motorola, Inc., combine to generate the communication protocol necessary to operate in a cellular system. The microprocessor 103 uses the memory 104 comprising the RAM 105, the EEPROM 107, and the ROM 109, preferably consolidated in a pack 111, to execute the necessary steps in order to generate the protocol and carry out other functions for the device. wireless communication, such as writing to a deployment device 113, accepting information from a keyboard 115, accepting input / output information by means of a connector 116 according to the present invention, controlling a frequency synthesizer 125, or carrying perform the steps necessary to amplify a signal according to the method of the present invention. The ASIC 101 processes the audio transformed by the audio circuitry 119 from a microphone 117 and towards a speaker 121. A transceiver processes the radio frequency signals. In particular, a transmitter 123 transmits through an antenna 129 using carrier frequencies produced by a frequency synthesizer 125. The information received by the antenna 129 of the communication device enters the receiver 127 which odulates the symbols by using the carrier frequencies from the frequency synthesizer 125. The communication device may optionally include a message storage and receiver device 130 that includes digital signal processing means. The storage device and message receiver could be, for example, a digital answering machine or a paging receiver. Turning now to Figure 2, a block diagram shows a receiver 127 for a dual band radiotelephone according to the present invention. An RF signal received by the antenna 129 is coupled to a coupling circuit 201 comprising a first RF coupling block 202 and a second RF coupling block 204. The RF coupling circuits are designed to provide the coupling of impedance appropriate to the receiver, depending on the frequency of the received signal. The RF signal is then coupled to an antenna switch 206 which is controlled by an antenna switch control circuit 208. The antenna switch control allows RF signals to be received and transmitted by an accessory coupled to the device communication via connector 210. For example, a hands-free accessory to allow hands-free operation in a vehicle to be coupled to connector 210 according to the present invention. The received RF signal is then provided to a plurality of receiver paths by a line 212. That is, a separate path will be provided for each band, depending on the number of bands available for the communication device. In particular, the line 212 is coupled to a transmission line 214 which provides the RF signal to a first filter 216. For example, the filter 216 could be a three-band band pass ceramic filter used as a filter preselector. For example, the ceramic filter could be tuned to pass RF signals from 935 to 960 MHz in the GSM reception band. The filter signal is then transmitted to a preamplifier 218. Preferably, the preamplifier 218 includes an enable line 220 for enabling or disabling the preamplifier. Preferably, the enabling line controls a transistor to provide isolation to the mixer of transmitter power and other false frequencies. The output of the preamplifier 218 is coupled to a combination filter 222 in a first input 224 and a LO injection frequency in a second input 226 by means of a transmission line 230 coupled to a controlled voltage oscillator 228. In the first trajectory, for example, a combined ceramic monoblock filter could receive 935-965 MHz in the GSM band and LO injection of 720-745 MHz. A common output port 232 of the filter 222 is coupled to a mixer 234 by means of a transmission line 236. The line 212 is also coupled to a second RF path by means of a transmission line 240 which is coupled to a second filter 242. The second filter could also be a band-pass ceramic filter. Three poles, for example, used in a preselector filter. The output of the filter 242 is coupled to a second preamplifier 244. Preferably, the preamplifier 244 also has a enable line 246 to provide isolation to the mixer of transmitter power and other false frequencies. The output of the preamplifier 244 is coupled to a second combination filter 246 at a third input 248. The combined filter 246 is also coupled to receive the LO frequency at a fourth input 250 via a transmission line 252. A combined output 254 is also coupled to the mixer 234 by means of a transmission line 256. As will be described in more detail in Figure 3, the mixer 234 generates an intermediate frequency (IF) signal at an output 258. The IF signal, the which is preferably 215 MHz, is provided to a filter 260, such as a bandpass filter SAW. Turning now to Figure 3, a circuit diagram shows mixer 234 of Figure 2. The mixer is designed to operate on a dual band radiotelephone, such as a telephone adapted to operate in both 1800 MHz DCS frequency bands. and GSM 900 MHz. The mixer's input circuit is designed to be coupled to 50 ohm in all bands and to filter the IF signal of 215 MHz output. Similarly, the mixer output circuit is designed with a 215 MHz filter-coupling circuit and a wide-band tape line LC deviation circuit to filter the input RF signals (for each band) to optimal performance of the mixer. In particular, the output signals of the combination filters are coupled to an inductor 302 of the mixer 234. The inductor is coupled to a capacitor 304 to ground and a transistor 308 to a base 310. An inductor 312 is also coupled to the base 310. Inductor 302 and capacitor 304 together with capacitor 306 and inductor 312 are selected to provide RF coupling at the inlet of the mixer. That is, the values are selected to provide an impedance of 50 ohms for each of the received bands, such as 900 MHz and 1800 MHz. Although other values could be employed within the scope of the invention, the inductor 302 is preferably approximately 3.3. nanohenries (nH), capacitor 304 is about .5 picofarads (pF), capacitor 306 is about 2 pf, and inductor 312 is about 5.6 nH. The collector 314 of the transistor 308 is coupled to a transmission line 318 that is coupled to ground by means of a capacitor 320. The collector is also coupled to a capacitor 322, which is coupled to an inductor 324 to ground and to the filter 260 Finally, an inductor 326 is coupled between the collector 314 and a resistor 332 coupled to an inductor 312. The capacitor 322 and the inductor 326 are selected to provide impedance matching to the IF 260 filter. The values of a ribbon line 318 and the capacitor 320 are selected to provide an LC bypass circuit to filter the RF input signals for optimum mixer performance. In particular, the values are selected to provide a low impedance at the output in order to prevent RF signals from passing to the filter 260, and providing a clean IF signal to the filter 260. For a dual-band radiotelephone receiving signals from RF of 900 MHz and 1800 MHz, the tape line 318 preferably has an amplitude of approximately 20 mils and a length of approximately 350 mils, providing an inductance of approximately 3 nH. The capacitor 320 is preferably a capacitor of 4.7 pF, while the inductor 326 is approximately 27 nH. Finally. The mixer is designed to provide an IF coupling to the filter 260. The inductor 326 and the capacitor 322 are preferably selected to provide low impedance at the IF frequency of the mixer. For an IF frequency of 215 MHz, the capacitor 322 is approximately 33 pF while the inductor 326 is approximately 27 nH. Similarly, an IF bypass is provided to prevent the intermediate frequency from backing up to the transistor 308. In particular, a capacitor 334 coupled between the inductor 312 and the ground provides a bypass for the IF signal. For an IF frequency of 215 MHz, the inductor 312 is approximately 5.6 nH and the capacitor 334 is approximately 68 pF. In a triple band radiotelephone, an additional RF path can be provided to receive signals from a third communication system. For example, the communication device could also be adapted to receive signals from PCS 1900. In particular, in Figure 4, line 212 could be coupled to a third RF stage by means of transmission lines 451 and 414 which are coupled to a filter 416. For example, filter 416 could be a three-band bandpass ceramic filter used as a preselector filter. The ceramic filter could be tuned to pass RF signals to 1930-1990 MHz in the PCS reception band 1900. The filtered signal is then transmitted to a preamplifier 418. Preferably, the preamplifier 418 includes an enable line 420 for enabling or disable the preamplifier. Preferably, the enabling line controls a transistor to provide isolation to the mixer of transmitter power and other false frequencies. The output of the preamplifier 418 is coupled to a combination filter 422 in a fifth input 424 and a LO injection frequency in a sixth input 426 by means of transmission lines 430 and 452 coupled to a controlled voltage oscillator 228. The output 432 of the filter 422 is coupled to the mixer 234 by transmission lines 436 and 453. Although three steps are shown in the present invention, additional steps may be employed as necessary depending on the number of networks to which it is accessed. Turning to Figure 5, a circuit diagram shows mixer 234 of Figure 4. The mixer is designed to operate in 900 MHz frequency bands of GSM, 1800 MHz DCS and 1800 MHz PCS in a triple band radiotelephone . The mixer input is designed to be coupled to 50 ohms in the three frequency bands and to filter the IF signal of 215 MHz output. Similarly, the mixer output circuit is designed with a 215 MHz filter coupling circuit in a broad band tape line LC deviation circuit to filter the input RF signals (of the three bands) for optimum performance of the mixer. The remaining portions of Figures 4 and 5 are identical to Figures 2 and 3, and the functionality of those sections will not be repeated here again. Although the invention has been described and illustrated in the foregoing description and drawings, it is understood that this description is given by way of example only and that numerous changes and modifications can be made by those skilled in the art without departing from the true spirit and scope of the invention. invention. For example, specific radiotelephone systems having specific reception bands are described. However, other systems, such as EGSM, are contemplated by the present invention. Although the present invention finds particular application in portable cellular radiotelephones, the invention could be applied to any portable device, including pagers, electronic organizers, or computers. Our invention should be limited only by the following claims.