Radio handoff between multiple wireless networks

The present invention relates to a wireless communications apparatus. Wireless communication device is configured to support the call to the remote communication device via the cellular network or an IP network. Wireless communication device is further configured to handoff the call between the cellular network and the IP network. An interworking unit (IWF) is comprised of a wireless communication device is to maintain the call between the wireless communication device and a communications device when a handoff between cellular network and an IP network.