Google’s Gmail email service already includes instant messaging along with voice and video chat. The company has now added conventional phone calls to the Gmail interface. This option is currently only available within the USA, although the company says its working on making this available more broadly. A special voice and video plug-in needs to be installed; it’s available for Windows, Mac and Linux computers.
Calls within the US and to Canada will be free for at least the rest of the year; calls to other countries cost from $0.02 per minute. Customers using the Google Voice VoIP service can also receive receive calls inside Gmail.
[Google blog]