Systems and methods for switching among heterogeneous networks and inter-working between a source access system and a target access system. An inter-system handoff control component can facilitate setting an IP tunneling by the mobile unit, wherein IP addresses for inter-working security gateway and Radio Access Network of the target access system can be identified. The inter-system handoff control component can then implement tunneling between the source system and the target system, wherein signaling/packeting associated with the target system can be transferred over the source system.