Facebook users in the US and Canada who are online with the service can now call each other for free on the main Facebook iOS app, a feature formerly restricted to the Facebook Messenger program. The feature, which works over both Wi-Fi and 3G/LTE connections, allows friends to start a chat session and then change it into a voice call. Currently the feature works with the iPhone or iPod Touch version of the Facebook app only, but should arrive to the iPad version through an update expected soon.
