This would seem useful if you could do it over 3G. As someone mentioned, that's been done in Europe for something like 5 years.

Otherwise, being able to video chat over wifi -- skype (and ichat, though ichat seems much more picky about firewalls) has done that for years, too. Yeah, true, now you'll be able to do it without your laptop (but still have wifi), but it's not like it's some kind of revolutionary leap...