Perhaps we'll have a system akin to DNS that resolves phone numbers to IPs. Dynamic DNS functionality could be built-in or layered on top by a provider like Google Voice, so that you don't give up one-number-that-follows-you.
Whichever device you happen to be using notifies you of the call.
Really though, the whole notion of calling someone and demanding their immediate attention is often rude in these modern days of async communication. I wouldn't be sad if we just used phones less, since we already have chat, im, and email that already just arrive to the device we're using (or all of them). And SMS on phones.
This sounds exactly like Facetime. They resolve your call by phone number or email. I hope they release it to IETF (like Steve said they would do) or a competent competitor comes along that can do the same. I've been trying to like SIP but the headache you go through to place a true SIP call is incredible.
* Your +SIPnumber@SIPdomain.com
* Your +SIPhandle@SIPdomain.com
Placing a SIP call isn't a problem. But all the cockups are in the receiving or finding people to call.
Whichever device you happen to be using notifies you of the call.
Really though, the whole notion of calling someone and demanding their immediate attention is often rude in these modern days of async communication. I wouldn't be sad if we just used phones less, since we already have chat, im, and email that already just arrive to the device we're using (or all of them). And SMS on phones.