As reported in the beginning of June, Google now officially announced the addition of Voice calls in Gmail.

The option to “Call phone” now appears within Google Chat. When you click the link, a Gchat pop-up appears where you can dial numbers and make phone calls.

Voice cancellation technology minimizes echo.

You can receive phone calls in your Gmail with your Google Voice number.

You can switch between your cell phone and Gmail, which is useful if you have bad cell coverage or a bad Internet connections.

Phone calls in U.S. and Canada are free, and calls to most countries cost $0.02.

And finally there a small video that shows Google Voice in Gmail

Source: Mashable.com