Patent ID: 7620411

Claim:
A mobile station which (i) monitors, in a monitor cycle, a paging channel slot which stores a message therein and is transmitted by a radio base station in a transmission cycle, and (ii) performs a process according to the message, comprising: a PTT setting reception unit for displaying on a display on the mobile station that the mobile station is in a normal idle mode for performing a communication with use of circuit switching for determining when a voice packet communication for the normal idle mode is available, and for receiving a PTT setting instruction for setting a PTT (Push to Talk) mode in which a voice packet communication for the PTT mode is available, the PTT mode operating, at the same time as the normal idle mode, for allowing the determination of when the voice packet communication for the normal idle mode is available while the mobile station is in the PTT mode; a monitor cycle switching unit for switching, when the PTT setting reception unit receives the PTT setting instruction, the monitor cycle to a predetermined short cycle which is for the PTT mode, the predetermined short cycle being shorter than cycles for other modes; and a voice reproduction unit for receiving a voice packet which is transmitted from the radio base station after a PTT CALL is detected in the message, and for reproducing a voice based on the voice packet, the PTT CALL being a request for the voice packet communication for the PTT mode.