Centralized call accounting equipment interrupts a scanning routine to seize a storage compartment in which it registers initial call and charge data presented by an originating register, the storage compartments being normally processed in sequence to update call charge particulars in accordance with the call state as monitored from an associated junctor, call particulars being transferred at the end of a call to a recording device. As shown in Fig. 4, the centralized accounting equipment has a ferrite core storage matrix 8 with input and output registers 9, 10 fed from and feeding buses 11 and 12. An address routine is obtained with an advance input 17 to an address store 13 in association with address register 18. Call Charging is effected in a circuit 14 in accordance with instructions in a store 19. The matrix provides storage compartments for 1000 calls. An additional 15 compartments form a transit section 23 used to hold completed call data in suspense before it is recorded. Recording is made on a tape machine BM by way of a buffer 15. If a ticket of call particulars is required, this is produced, without use of the transit section, by using buffer 16 and teleprinter ME. Particulars include the numbers of the calling and the called parties, the date, the time of completion, the call duration, and the call charge. A further 9 compartments are available, one of which is used to record the address of the last scanned free compartment for allocation to the next occurring call. Input data is relayed by way of a so-called programme apparatus P and is derived from a junctor connector TJ (providing according to addressed instruction a particular junctor free/busy signal E and the junctor metered/not metered signal F) and from a register connector CE which identifies registers with initial call data and demands a programme apparatus P input routine. If the equipment has no free storage compartment, a bi-stable 55 is set to block gate 2 and consequently ignore register connector requests until a storage compartment falls free. Junctors of the exchange network are arranged in groups of 500 which are served in duplicate by two call accounting equipments of which Fig. 4 shows an individual one. Each junctor connector of an associated accounting equipment can interrogate a group of 500 junctors in an immediately associated junctor group in common with a junctor connector from a next accounting equipment the immediately associated junctor group of which is similarly interrogated in common with a further accounting equipment, and so on. Registers are grouped according to the associated junctor groups and are similarly served by both the immediately associated and a next accounting equipment. Registration of call data is made in duplicate in each of the two accounting equipments accessible to a call. The records of both equipments may be read out to the magnetic tape stores on completion or the record of only one equipment may be read out in accordance with a status bit recorded along with the call particulars to indicate that the equipment is on-line or is stand-by to cover the presence of a fault in the other. Out of a sequence of register connector circuits CE1 to CEn the circuits CE3, CE4 are shown in Fig. 5. Registers E, one from each of the groups associated with the connectors, have relays AL, AR, AT for communication with their immediately associated connectors, and have relays BL, BR BT for communication with their next associated connectors. Given the calling and called subscriber numbers, the identity of the junctor serving the call, the metering rate, and the calling class of service, registered in a store 39, a register operates a relay A to bring up service demand relays AR and connector circuits scan terminal groups 26, 27, in search of service demands, such a demand halting the scan by a signal over gates 30, 35 and 28. Gates 30 also revert a send signal to operate relay. AT or BT so as to couple the call data in store 39 of the register to a store 47 in the connector. A delay 37 responds after the initial demand signal from gate 35 to pass a signal over gate 49 on lead .1 to the programme apparatus to request an interruption of the scanning routine in order to transfer the call data to a free storage compartment in the matrix 8. When apparatus P has received the data and stored it, a signal is reverted to trigger monostable 50 which has the effect of operating relays AL, BL to release the register relays A and so discontinue the demand signals. Storage compartments in the matrix 8 of the accounting equipment each comprise 8 words of 26 bits each. The first word holds the identity of the junctor in use for the call being metered, the calling subscriber's class of service code, a code number indicating the subprogramme relevant to processing at any particular time, and a bit indicating whether the compartment is the on-line compartment or a stand-by compartment for which no recording on magnetic tape should be made. Another word holds the charge rate code and bits employed as a timing counter for measuring off pulse lengths and marking out intervals. Further words hold the calling and called subscriber numbers, a call duration count with a capacity of 100 mins., and a total call charge count. Processing of compartments is based on the sub-programme contained in the first word of each compartment. If the sub-programme code is O the compartment is free. As each free compartment is scanned its identity is written into the store section which indicates the next compartment to be used for a call. Sub-programme with code 1 indicates that call particulars aie registered, but metering is not in force, the junctor for the call being interrogated to establish E and F states to see if and how the programme should be advanced. If the junctor is in the ringing state no action is taken unless the on-line compartment is faulty in which case the stand-by compartment has its status bit switched to on-line. If the junction exhibits called party reply a grace period of 15 seconds is introduced by a sub-programme with code 2 in which the mode of charging is also established. If the call is charged by one fixed amount, this is determined and the programme is advanced to ticketing and registering on tape if the compartment status bit indicates that it is on-line. If the junction supplies inconsistent signals to interrogation, the sub-programme coded 8 is called for to place the compartment out of order and initiate testing of the junctor. If the call is charge according to duration subprogramme coded 3 is entered to effect production of the call duration count. When release is detected, sub-programme coded 4 is taken up to test the release condition for persistence. If release is not confirmed, the sub-programme immediately preceding the spurious release is reinstated. If release is confirmed, the programme is advanced to issue a ticket, if the calling class of service code so requires, by transferring call particulars direct to the teleprinter buffer. The sub-programme is otherwise advanced after release, or after ticketing, to transfer call particulars to a free transit storage compartment pending it accumulation on the magnetic tape store BM. The compartment sub-programme code is now set to O indicating idle condition. At the end of each processing cycle over the compartments a sub-programme coded 7 is entered to transfer all call data in the transit storage compartments to the magnetic tape store BM. If, on call completion, no transit storage compartment is free, the call compartment requiring its particulars to be transferred has sub-programme code 7 recorded in its first word so that it is ignored during scanning until a transit compartment falls free. Instead of transferring all call data to a transit storage compartment an address may be registered so that the call compartment is accessed direct for transfer to the magnetic tape store. If no grace period is allowed for called party recognition, the sub-programmes coded 1 and 2 are combined as a single programme. Subprogrammes are provided for maintenance checks and tests.