The next generation of communication networks is expected to create a heterogeneous network environment encompassing an ever-increasing number of different access networks and end-user terminals that will enable the introduction of and provide access to numerous feature-rich end-user services. It is essential that end users be able to roam from one access network to another if they are to enjoy a seamless roaming experience, which is especially important for multimedia applications such as voice, audio, and video. This paper describes how to make such a roaming experience possible in multimedia applications based on Session Initiation Protocol (SIP). It also describes several mobility management solutions and compares the suitability of SIP sessions for roaming across General Packet Radio Service (GPRS), Universal Mobile Telecommunications System (UMTS), and wireless local area network (WLAN) networks. The comparison is based on the implementation of a prototype. The advantages and disadvantages of each mobility management solution are discussed, as are the issues encountered during the implementation of the prototype. © 2004 Lucent Technologies Inc.