A mobile telephone system has a base transceiver station (BTS) that provides radio communication with a mobile handset (MS) and also communicates with a control station (BSC) through a communication link in the form of a leased line which provides a first communication path with a predetermined bandwidth for signals communicated between the BTS and the BSC. A communication network in the form of an ISDN is used to provide a selectively connectable second communication path between the BTS and the BSC so as to augment the bandwidth available for the signals during periods of peak demand. In order to accommodate different call connection times in the system through the leased line and the ISDN, the BSC/BTS are arranged to produce all connection signals that initiate billing at the same time irrespective of the path used to make the call connection.