In the session-initiated protocol (SIP) for wireless networks, delays and disruptions that occur during the handoff of nodes are related to authentication, authorization, and accounting (AAA). Various schemes have been proposed to reduce these handoff delays, and one such proposal, shadow registration in adjacent cells, has been adopted. Shadow registration reduces handoff delays by preregistering a cell with all of its neighboring cells. However, preregistering with multiple adjacent cells significantly increases both the amount of network traffic and the corresponding waste of network resources. This paper introduces region-based shadow registration (RSR) for efficient mobility management in mobile SIP environments. The proposed scheme performs shadow registration with neighboring cells selectively, only when it is necessary at the FAAA level. In an experiment implementing the system, we show that it reduces handoff latency while decreasing excessive signaling traffic during shadow registration.