Fantastic news. Google is supporting SIP as a part of Google Voice! No more proprietary protocols here folks!

http://www.ubergizmo.com/2011/03/voi...-google-voice/

LINK: Call a google voice number via SIP (bypass PSTN)

Free calls for everyone!

Soon a call will be simple calculated in terms of data consumed -- next to nothing.

I can see this feature being extremely useful for businesses. It's cheap, and because of Android handset proliferation, provides a very easy avenue for internet telephony on handsets.