Many people are interested in using Google Voice together with a software PBX and there is an option. Google Voice let you forward your voice to a gmail chat account (the one with the same user id as Google Voice). Now this is interesting as with the right software you can integrate it via the Jabber/Xmpp.

PBXes has done it and there is talk that Asterisk 1.8 will do it 🙂

I’ve not tried any of them, but it sure sounds good ….