The standards bodies have defined the interworking architecture between 3GPP LTE/SAE and 3GPP2 EV-DO. For inter-system handoff, pre-registration and pre-authentication are performed to establish the required resources before the actual handoff. However, the standards only define the handoff procedures without specifying when to reserve or release the resources, which include sessions, bearers, user context information, and so on. In this paper, we propose Resource Reservation and Preemption (RRP) to determine when to release the reserved resources of the preregistered/pre-authenticated users. If the user moves back and the resources still exist, the signaling cost for the preregistration can be minimized. Simulations are conducted to evaluate the performance of the proposed RRP. The results show that the RRP can reduce handoff signaling cost effectively.