From the Google’s official blog, Google announced free calls from anywhere in the world to US and Canada for free.
This feature will be available in You gmail account. You will see the “Call phone” link below the regular chat bar.
and the Voice and Video chat from:
Then you’ll need to download a dmg file from here.
Then you’ll have to accept the terms set by Google.
Then you’ll be able to call US and canada for free.
Official Video from Google.