IMS (IP Multimedia Subsystem) couldn't miss such event. Seen as evil for the freedom of IP world, the way Telcos can restrict mobility, or, actually, to charge for it.
Joachim Fabini of Technical University of Vienna, shared his experiences while implementing a OpenSER-based IMS in CAMPARI project (interesting concept: IMS in a bottle). Along with the architecture and components, very valuable were his conclusions and thought about IMS and future directions of VoIP, where the mobile communication will meet IP world and directions to be approached to ensure success.
A very interesting result of this experiment was that they used OpenSER barely as it is, with no hacking, IMS components being OpenSER instances with different config file. The work was a proof of concept, optimization could be brought by code writing.
Download slides of OpenSER IMS.