Personalisation portability

I had an interesting thought during an IMS (IP Multimedia Subsystem) presentation at an industry event today... if operators (fixed or mobile) start to act as aggregation points for "user identity" (ie linking together your service subscriptions, phone #s, IM accounts and so on), will users face absolute lock-in with their contact lists / buddy lists etc? This certainly seems to be one of the possibilities / threats being posited about IMS-based networks & applications.

Does this mean that you will have to accept you have an "operator for life"?

Or will there have to be cooperation (or laws) about "personalisation portability"? (in the same way I discussed the lack of email portability recently). How would this work?

Or will users be better off with (free) "operator independent" Internet-based identity hubs like MSN, Google or Yahoo!