HP and Atos Origin jointly released to Open Source an IMS testing tool called Seagull (http://gull.sourceforge.net/). It continues the legacy of the successful sipp, which has proven valuable for SIP compliance testing and benchmarking.
Seagull is an extensible tool with immediate support for key IMS protocols such as Diameter, XCAP, and TCAP.
This is a very exciting development, because it will accelerate interoperability between IMS component vendors. I am hopefull that a critical mass of community support will build up around it to ensure long term viability of the project and a growing library of IMS testing plug-ins.