Facebook on Wednesday started offering free voice calling in the U.S. through the Facebook Messenger app for iPhone. The service is an extension of the VoIP in Messenger test Facebook started rolling out the first week of the year and is currently available in the U.S. and Canada.

In order to test the new feature, you'll need to first download the Facebook Messenger app on your phone. You'll be able to make free calls to persons who are also using Messenger for iOS.

Of course, the call it totally free only if you are using Wi-Fi - calling over 3G or 4G networks means you'll have to pay for the data usage.