Abstract: A mobile unit generates and collects call detail record information relating to the usage of a mobile cellular telephone system which is compatible with conventional telephone devices. A communications interface transfers the call detail record information to a stationary unit containing a computer and an evaluation program. The computer and its evaluation program evaluate the usage of the mobile cellular telephone system. The invention may be used to provide billings for rental use of a cellular telephone, to verify cellular telephone billings, and in other applications requiring monitoring of the usage of a cellular telephone system. The evaluation program used to evaluate the call detail record information is independent of the microprocessor and program used for the call detail record information generation and collection. The evaluation program may be very complex so as to tailor the evaluation of the call detail record information to the exact needs of an application.