Abstract: A packet communication card enables consumption of a battery for a portable digital telephone to be reduced by changing supply power for the portable digital telephone in accordance with a state of the portable digital telephone. The pocket communication card which is connected to the portable digital telephone, and which is provided with a COM port necessary for implementing packet communication, is inserted into a data terminal equipment to be used. There is reduced consumption of the battery for the portable digital telephone by selecting to be changed one power source which is a power source of power sources being at least more than one for supplying power to the portable digital telephone in accordance with state of communication of the portable digital telephone. A switch implements change of supply power.

Abstract: In order to detect the history of movement and current position of a radio set, a mobile communication system stores the current position of movement of a radio set as registered position information together with the position in which the radio set was previously located. The radio set transmits a registered position information request signal when registered position information is requested. When the radio set system receives such a request signal, it transmits to the radio set the registered position information that was stored. The radio set receives and stores this registered position information and displays it on a display unit.