Looks like 3GPP members are thinking about extending IMS Centralized Services with a new feature, Inter-Device Transfers. Nomor's September 2008 3GPP news made me aware of SP-080507 which contains the work item description for gathering requirements for this feature to allow an ongoing media session to be moved from one device to another.
An interesting feature I can see many uses for. When coming home, I transfer an ongoing call from my mobile to a desktop phone with better hands-free support. Or, when I enter the car, I transfer the call from the mobile phone to the car's system, maybe dropping the video component that was part of the call in the proccess. After all, one should look at the road.
Maybe they were inspired a bit by the DAIDALOS project which has worked on such scenarios already a couple of years ago. Also, such Inter-Device transfers are interesting for converged fixed/mobile operators who could offer such services to the customer over their integrated network.