Patent ID: 7283833

Claim:
A PTT (push to talk) system that includes a plurality of mobile phones including PTT capability and a display unit, and a server which mediates a PTT call between mobile phones, the server comprising: a storage unit stores a phone identifier of a mobile phone and an image related to the phone identifier; a retrieval unit retrieves the image from the storage unit; and a sending unit sends the image retrieved by the retrieval unit to at least one mobile phone, wherein the display unit of the mobile phone displays the image sent from the server, wherein the PTT call is a group call between the plurality of mobile phones that belong to the group, the storage unit stores a group identifier of the group, the phone identifier and the image related to the group identifier, and the retrieval unit retrieves the image related to the phone identifier that belong to the group from the storage unit, wherein the server further comprising, a PTT mediation unit determines one of the mobile phones as a transmitting mobile phone, wherein the sending unit sends a phone identifier of the transmitting mobile phone to the at least one other mobile phone if the PTT mediation unit changes the transmitting mobile phone, and in the at least one other mobile phone, the display unit displays the image related to the phone identifier and makes a different display style from the mobile phone other than the transmitting mobile phone when the phone identifier is sent from the server.