Mobile IP is one of the popular mobility solution and a viable candidate for the Beyond 3rd Generation (B3G) networks such as the integrated 3rd Generation Universal Mobile Telecommunications System (UMTS) and the Wireless Local Area Networks (WLANs). Mobile IP has many configuration and enhancements that are proposed by IETF such as the Care-of-Address (CoA), Collocated CoA, Mobile IPv6, and route optimizations. In this paper, we present a side-by-side performance evaluation and comparisons of the UMTS to WLAN handoff delay that results from using each configuration in the lately adopted UMTS/WLAN interworking architecture by 3GPP. In addition, we analyze the delay components due to 3GPP security and Internet protocol integration requirements. Simulation results show that under low network loading all configurations yield similar performances. However, Mobile IP with IPv6 configuration is more sensitive for network loads and wireless access speeds. In fact, it produces the highest delay figures at high load. Moreover, 3GPP security procedures contribute to more than 60% of the handoff delay for all the configurations.