• Voice over IP
• Voip
• SIP Client
• IP Multimedia Subsystem
• IMS

The growth of the Internet and the great popularity of cellular phone systems is the background to this thesis. The thesis has been designed and developed at Siemens Mobile SPA labs in Milan within a partnership between Siemens and an Italian 3G Mobile Network Operator, the Exploit (EXPeriences on deveLOpment of Ims based applicaTions) project. The main tasks have been designing the IMS Exploit client and an audio call solution and their implemention. The idea behind the work has been the implemention of a flexible common application that would perform Instant Messaging, Chat, Presence and Voice over IP and manage the messaging for multiple services on its top.The Voice over IP solution is integrated in the Exploit client and permits users to perform calls from the same environment, while using one of the available services.The reasons that have led to this design and implementation are the demand of having a SIP messaging behavior aligned to RFC 3261 and of providing an open interface over which new services may be deployed.