Facebook has been on a real push to take over users' phones as of late, with Facebook Home, Chat Heads, and updates to its official and Messenger apps. Today, it goes a step further, offering full, free voice calls to US users. This is the same feature that rolled out to Canadian users late last month.
The service requires Facebook Messenger to be installed (naturally) – to initiate a call, simply head into your contact list, open a message, and hit the "I" in the top-right corner. You should see an option for "Free Call" in the list; if it's white, the users can receive a call. If it's gray, then your friend can't receive calls. Simple enough.
This new feature doesn't require an app update and should be rolling out to users now.
via The Verge