Google 
now supports the ability to make phone calls from Gmail. Calls to the U.S. and Canada will be free for at least the rest of the year and calls to other countries will be billed at set rates. The service is being rolled out to U.S. based Gmail users over the next few days.
As a marketing ploy, Google also plans to put its free phone service in traditional “red box” phone booths that will be deployed in airports and at universities. These will give people to try out the voice quality of its calls.
http://www.google.com/chat/voice/
