To easily transmit and receive a mail between portable telephone terminals by allowing a calling side to transmit a message to which a specific pattern is added and to transmit character data through a voice communication channel when a message to which a specific pattern is added is transmitted from a call incoming side, and allowing the call incoming side to process the data received through the voice communication channel as the character data.

A portable telephone terminal at a calling side adds, for example, 'SI' and 'SO' patterns to a calling number communication message. When the 'SI' and 'SO' are included in the received calling number communication message, a portable telephone terminal at a call incoming side adds 'SI' and 'SO' to the calling number communication message, and returns this message. When the 'SI' and 'SO' are included in the transmitted calling number communication message, the calling side transmits character codes stored in a memory 55 at the calling side through a traffic channel. The call incoming side stores the transmitted character codes in a memory 55 at the call incoming side, and displays them on a display 53.