Method and apparatus in a wireless communication system for facilitating a handoff

A dual-band wireless subscriber unit (SU) having an enterprise address of E and a cellular address of C, corresponding method, software program, and WLAN determines that the SU is about to leave a wireless local area network (WLAN). In response, when the SU is involved in a call on E, the SU sends to the WLAN a SIP message, for example a Refer message with a "Refer To" field of C if an ongoing call or a SIP Redirect message with a contact address of C if a new call is attempting to begin on E. In response to receiving either message, the WLAN seamlessly transfers the call to C