Facebook today updated its iOS app to include free user-to-user calling. The feature launched one month ago inside Facebook's standalone Messenger app, but has now been graduated to the company's primary app, which has a much larger install base. This means that the tens of millions of people who have Facebook installed on their iPhones can now make and receive calls over Wi-Fi or a cellular data connection. To make a call to another Facebook user, all you need to do is open a chat with that person, tap the "i" button in the top-right corner, and tap Free Call.

While Facebook for iOS works on both iPhone and iPad, it appears that free calling hasn't been activated for Apple's tablet. It's also worth remembering that free calling only works in the US and Canada, though we'd expect it to roll out to other countries at some point in the future. Now that Facebook for iOS includes the feature, there's one less reason to use an app like Vonage, Skype, or Viber to call friends and family nearby. While not everyone likes Facebook, its massive mobile install base means this feature has a real shot at widespread adoption.