A telephone terminal provided with a plurality of transmitter/receiver units and a base unit. When receiving an incoming call based on identifying information through Internet, the telephone terminal calls the transmitter/receiver unit to perform a voice call only if the voice call through the transmitter/receiver unit of the identifying information is available. When receiving the incoming call based on IP address through Internet network, the telephone terminal determines whether or not the voice call through the transmitter/receiver unit, to which identifying information is assigned, is available. Only if the voice call is available, the transmitter/receiver is called and the voice call is performed with a calling party through Internet network. If the voice call is unavailable, the message indicating that the voice call is unavailable is output to the calling party.