Patent ID: 8340673

Claim:
A communication network for providing call delivery to a dual mode wireless device, the communication network comprising: an IP Multimedia Subsystem (IMS) network operable to serve the dual mode wireless device; and a cellular network operable to serve the dual mode wireless device; the IMS network includes a call control function that is operable to receive a call to the dual mode wireless device, and determine that the dual mode wireless device is registered in both the IMS network and the cellular network, responsive to the determination that the dual mode wireless device is registered in both networks, the call control function is further operable to transmit a SIP OPTIONS message to the dual mode wireless device over the IMS network to determine if the dual mode wireless device is available over the IMS network for the call, and transmit a call setup message to the dual mode wireless device over the IMS network to attempt to set up the call over the IMS network responsive to receiving a response to the SIP OPTIONS message from the dual mode wireless device; the call control function is further operable to transmit a call setup message to the dual mode wireless device over the cellular network to attempt to set up the call over the cellular network responsive to not receiving a response to the SIP OPTIONS message from the dual mode wireless device.