Stating today, Google allows calling to regular phones from Gmail. From a desktop browser, user can place calls to the U.S. and Canada will be free for at least the rest of the year. International calls will be billed at low rates. Example: calls to the U.K., France, Germany, China, Japan—and many more countries—for as little as $0.02 per minute.
Dialing a phone number works just like a normal phone. Just click “Call phone” at the top of your chat list and dial a number or enter a contact’s name.
If you have a Google Voice phone number, calls made from Gmail will display this number as the outbound caller ID. And if you decide to, you can receive calls made to this number right inside Gmail (see instructions).
Google is rolling out gradually this feature to U.S. based Gmail users over the next few days, so you’ll be ready to get started once “Call Phones” shows up in your chat list (you will need to install the voice and video plug-in if you haven’t already).
[Source Google Gmail Blog]