With the increasing demand of the mobility of mobile users, seamless handover is a critical issue for heterogeneous network accesses. Improving the blocking probability of SIP calls resulting from the handoff delay is a key issue for achieving seamless handovers across WLAN and cellular networks. This paper presents an efficient scheme, based on intelligent agents, to support pre-authentication for seamless handover, where the intelligent agents are able to cooperate with each other adaptively. Besides, intelligent agents offer the applicability of key distribution with EAP-SIM based AAA protocols to enable fast authentication for inter-domain handovers. The paper proposes a number of possible changes to these solutions for inter-domain operation. In addition, simulation results show that the proposed intelligent-agent-based handoff scheme is capable of improving the performance of the existing handover in call blocking ratio, packet loss ratio and call interruption ratio, so as to reduce the signaling traffic in wireless networks.