Abstract: A self-diagnostic system for a checking all functions of a cellular-transceiver system having a cellular-interface unit, which interface unit couples a standard telephone set to a cellular transceiver, which interface unit converts the DTMF or pulse-type of dialing signals into digital format for transmission to the cellular transceiver, whereby the dialed number made on the land-type of telephone may be used to call a number over the cellular system. The present invention not only monitors and checks the proper functioning of the transceiver and associated power supply, and the like, but will also monitor and check the interface unit.

Abstract: An interface unit for coupling an international-type pay-telephone to a land-based or cellular telephone system. The interfacing unit of the invention has a microcomputer, and an associated EPROM in which is stored the exchanges of the telephone numbers that are accessible by that local payphone-terminal, which EPROM also stores a table indicative of the tariffing rates associated with the respective exchanges called. The invention also includes the tone-detectors for detecting the dialed DTMF digits of the pay-telephone, for the conversion thereof for storage in the microcomputer for the determination of a valid telephone number dialed in order to determine the associated tariffing rates. The tone detectors also detect the tone-signals received from the telephone system. The invention also includes "isolating" switching circuitry for isolating the coin-operated pay terminal from its couplement to the telephone system until the telephone call has been connected.