The use of open protocols combined with fast and cheaper Internet connections will ensure continuous growth of the Internet services and applications in the next decade. The IP Multimedia Subsystem (IMS) was introduced by the Third Generation Partnership Project (3GPP) in 2002 to enable mobile systems to provide ubiquitous cellular access to all the services that the Internet provides, with improved QoS, appropriate charging and integration of different services. IMS is a promising candidate to drive the telecommunication network towards Next Generation Networks. This book presents the development of IMS Client compliant to the 3GPP Standard. While similar work has been going on for the development of the IMS Client by other researchers, such clients were found not to address memory and processing power which is limited in mobile devices. The IMS Client was developed using the Java 2 Micro-Edition environment, which is the most suitable development platform for smart mobile devices. The developed IMS client should be useful to the telecommunication or ICT students and engineers who may be interested in the exploration of next generation applications for smart mobile devices.