A method and apparatus for session continuity using pre-registration tunneling procedure are disclosed. For session continuity, a tunnel is established between a multi-mode wireless transmit/receive unit (WTRU) and a core network of a target system via a source system while the WTRU is still connected with the source system. An access procedure is performed toward the target system using the tunnel. A handover is the performed from the source system to the target system once the access procedure is complete. The access procedure includes session initiation protocol (SIP) registration, authentication of the WTRU at the target system, and internet protocol (IP) configuration. The handover may be from a third generation partnership project (3GPP) system to a non-3GPP system, or vice versa.