es the same applications to be deployed over fixed and mobile networks. TISPAN Working Group 6 (the competence center for testing within TISPAN) manages the development of testing specifications for NGN. With ETSI TISPAN NGN Release 1 focused mainly on the wireline world, the main concern for interoperability and testing is migrating legacy circuit switched networks to future NGNs using 3GPP IMS. The Open Mobile Alliance (OMA) standards consortium has defined application enablers that use 3GPP IMS [8]. Currently, OMA is the only standards body running interoperability tests as a major part of its enabler approval program, including enabler specifications for applications over 3GPP IMS. The challenge with the most impact for the SIP-based service enablers at the test fest is the provision of a reliable and interoperable IMS infrastructure. To ensure the interoperability of OMA service enablers, the interoperability of IMS systems in different providers' networks is also crucial to ensure that the required functions are working properly. The Alliance for Telecommunications Industry Solutions (ATIS) Packet Technologies and Systems Committee (PTSC) is building on the IMS framework for wireline networks in the US. Several IMS implementations exist, but due to the lack of an exhaustive testing program, interoperability issues are still found, forcing new IMS implementations procedures and rendering several existing implementations obsolete. All major standards bodies including 3GPP, 3GPP2, ETSI TISPAN, and OMA have recognized this challenge and are addressing the need for testing the interoperability between implementations of standards. It is understandable that it is difficult to exercise a complex platform such as IMS without applications using it. To circumvent this problem, exhaustive conformance test tools, capable of testing all specification parts and simulating realistic usage of the platform, must be developed. Common IMS In 2007 it was agreed that 3GPP would take overall responsibility of IMS specifications 