Cordless radio telephone system with a plurality of portable units

The system has a base station 20 which can communicate with a plurality of portable units 21 to 25 each having a unique ID number. When an incoming call is received from a telephone line connected to base 20, an answering voice message is sent to the caller from the base 20, the message including the ID's of all the portable units. The caller then selects a particular portable unit by sending DTMF signals corresponding to the required ID. The base 20 detects the required portable from the DTMF signal, scans channels to find a free channel, and transmits the ID of the required portable on the selected channel. Each portable scans channels to find a channel with a signal strength above a reference level, then if the signal on the selected channel includes its own ID the portable operates a bell or buzzer to alert the user and transmits an acknowledge signal to the base 20 in response to which the base establishes a call mode. By operating certain buttons, a portable can be set in locked state which is registered with the base 20. If the base receives an incoming call for a portable which is in a locked state, it sends a voice message indicating that this portable is in a call denial state. To set up a call from a portable, the portable scans channels for a free channel, indicated by signal strength below a reference, and then transmits its ID on the selected channel, and the base scans channels to find one with a signal strength above a reference, and then determines if the signal in the selected channel includes the ID of one of the portables.