The future of Google voice is here: Google adds voice calling to it’s Hangouts app

It’s always good to keep a promise and so has Google done today by rolling out it’s voice calling feature through its Hangouts messaging service. There is no difference between voice and video calling in terms of operation and use in the new hangouts as it will be able to work in Google+, Gmail, or the Chrome
extension, and the barmy Hangouts effects are even in play — although here it allows you to call phone numbers. As expected calls are free to the US and Canada, no matter what country you’re calling from, and impressively cheap elsewhere around the world.

source: Gmail Blog