This paper presents an experimental framework for implementation of an IMS/NGN reference service scenario by means of open source software. Multiple service enablers are deployed to build this service scenario. Interoperability tests between the deployed IMS entities and user equipment are carried out, as well as performance measurements of signaling overhead and delay of different IMS procedures involved to support the service scenario. Then, some preliminary results are obtained. After that, the IMS prototype is integrated with in-lab UMTS/HSDPA and WLAN networks to test IMS procedures in more close-to-real environment. Additionally, practical experiences with the IMS testbed deployment are discussed.