Patent ID: 8331340

Claim:
A method for use by a mobile communication device in facilitating voice calls through a wireless local area network (WLAN) and a cellular telecommunications network, the mobile communication device having a Session Initiation Protocol (SIP) identity for identification in the WLAN and a telephone number for identification in the cellular telecommunications network, the WLAN including a SIP proxy server and a gateway which is connected to a telephone network, the method comprising: operating in the WLAN for Voice over IP (VoIP) communications, including: registering with registrar server functionality of the SIP proxy server with the SIP identity, the SIP identity being further communicated to a location server; in response to an incoming voice call from a caller via the telephone network, receiving an INVITE request which is issued from the gateway and forwarded from the SIP proxy server, and sending a response to the SIP proxy server which is communicated to the caller via the gateway; when switching communication operations from the WLAN to the cellular telecommunications network: sending, via the WLAN to the location server, a message for forwarding voice calls directed to the SIP identity of the mobile communication device to the telephone number of the mobile communication device; and sending, via the cellular telecommunications network, a message for canceling the forwarding of voice calls directed to telephone number of the mobile communication device to the SIP identity of the mobile communication device.