Abstract: Provided is a mobile station that a user is able to use without inconvenience, and that is able to realize power consumption saving. The mobile station: records a speech-communication history including information identifying a time at which speech communication occurred; decides a cycle changing time and a cycle-after-change based on the speech-communication history, the cycle changing time being a time at which a paging channel monitoring cycle used by a base station in message transmission is to be changed, and the cycle-after-change being a cycle at which the paging channel is to be monitored after the change; notifies the base station of a slot cycle index indicating the decided cycle-after-change when the decided cycle changing time has come; and starts monitoring the paging channel at the decided cycle-after-change when the decided cycle changing time has come.

Abstract: To provide a PTT system that includes a plurality of PTT-capable mobile phones each including a display unit, and a server which mediates a PTT call between mobile phones out of the plurality of mobile phones. The server includes a storage unit, a retrieval unit, and a sending unit. The storage unit stores images of users of the plurality of mobile phones and phone identifiers of the plurality of mobile phones in correspondence with each other. The retrieval unit retrieves, from the storage unit, an image corresponding to a phone identifier of a mobile phone involved in the PTT call. The sending unit sends the retrieved image to at least one other mobile phone involved in the PTT call. A display unit in the at least one other mobile phone displays the image sent from the server.

Abstract: Provided is a mobile station that a user is able to use without inconvenience, and that is able to realize power consumption saving. The mobile station: records a speech-communication history including information identifying a time at which speech communication occurred; decides a cycle changing time and a cycle-after-change based on the speech-communication history, the cycle changing time being a time at which a paging channel monitoring cycle used by a base station in message transmission is to be changed, and the cycle-after-change being a cycle at which the paging channel is to be monitored after the change; notifies the base station of a slot cycle index indicating the decided cycle-after-change when the decided cycle changing time has come; and starts monitoring the paging channel at the decided cycle-after-change when the decided cycle changing time has come.

Abstract: To provide a PTT system that includes a plurality of PTT-capable mobile phones each including a display unit, and a server which mediates a PTT call between mobile phones out of the plurality of mobile phones. The server includes a storage unit, a retrieval unit, and a sending unit. The storage unit stores images of users of the plurality of mobile phones and phone identifiers of the plurality of mobile phones in correspondence with each other. The retrieval unit retrieves, from the storage unit, an image corresponding to a phone identifier of a mobile phone involved in the PTT call. The sending unit sends the retrieved image to at least one other mobile phone involved in the PTT call. A display unit in the at least one other mobile phone displays the image sent from the server.