My understanding is that Google's back end for click-to-call Chat utilizes XMPP in conjunction with SIP. They could reengineer the back end which they may have already done. Google also could shut it down for outsiders and not for themselves. Who knows? Not me! But, if you look at the direction Google is headed with Hangouts, I suspect the days of XMPP are numbered at Google, Inc. Keep in mind this all happened because M$FT was getting a free ride on Google's XMPP services without offering equivalent connectivity to their own services. I also think call forwarding with Google Voice will die sooner rather than later. It's costing Google lots of money with zero return. Does that sound like Google? We'll know soon enough. And it's anybody's guess, but that's mine. There's no reason to get blindsided. Everyone has had plenty of time to make alternative arrangements.