The wireline systems have moved to supporting richer voice over packet switched services with the introduction of Skype and Vonage type services. This has completely displaced the traditional circuit-switched services. This trend to move away from circuit-switched services is catching on in the cellular networks are moving towards supporting fundamental services like voice over the packet domain using the IMS over packet networks. In addition, there is widespread adoption of the wireless LAN systems at home, office and commercial environments. Cellular operators are seeing WLAN not as competing technology, but as something that complements it by allowing the offloading of MSs to the WLAN systems to increase the cellular system capacity and potentially extending coverage. Integrated WiFi and 2G/3G cellular is seen as having the best of two worlds, capitalizing on the strengths offered by each technology. Operators are equipping cellphones with WLAN capability and it was only natural to ask the question if the same applications supported over the packet domain in the wireline and cellular networks can also be supported over the WLAN systems.

This chapter discusses the topics of making WLAN systems interwork with the 2G/3G systems, service continuity between the two systems addressing domain registration and call continuity with emphasis on voice. This chapter is written covering the solutions as it applies to 3GPP2. Most of these solutions also apply to 3GPP and exceptions will be highlighted. This chapter is also written from a mobile device perspective since the device plays a central role in handling mobility between the different WLAN and 2G/3G technologies.