Patent ID: 7289816

Claim:
A method of setting up a Push-To-Talk-over-Cellular (PoC) call between a calling mobile station and a called mobile station in a Global System for Mobile Communications (GSM)/General Packet Radio Service (GPRS) cellular communication network, said method comprising: detecting that a calling user has selected a PoC contact list on the calling mobile station; responsive to detecting that the calling user has selected the PoC contact list, sending a presence refresh request message from the calling mobile station to a PoC server; responsive to receiving the presence refresh request message in the PoC server, sending an Unstructured Supplementary Services Data (USSD) message from the PoC server to the called mobile station; responsive to receiving the USSD message in the called mobile station: sending a USSD response message to the PoC server; performing a routing area update; and changing the called mobile station to packet mobility management state READY; detecting that a calling user has pressed a push-to-talk (PTT) button on the calling mobile station; responsive to detecting that the calling user has pressed the PTT button, sending an INVITE message from the calling mobile station to the called mobile station, wherein an access network serving the called mobile station delivers the INVITE message to the called mobile station without paging the called mobile station; returning a 200OK message from the called mobile station to the calling mobile station; and establishing packet flow between the calling mobile station and the called mobile station.