Isn't this what XMPP (the protocol google uses for gchat) is all about, at least for text? (c.f. http://en.wikipedia.org/wiki/Extensible_Messaging_and_Presen... )
Is A/V over XMPP standardized?
Is A/V over XMPP standardized?
Even so, I suspect it will be a long time before Skype, Apple, and everyone else does anything but try to set their own standards.