How do I make free phone calls with my iPhone using Facebook?

How do I make free phone calls with my iPhone using Facebook?

To use the free voice calling feature on the Facebook Messenger app, just tap the "i" icon in the top right hand corner while viewing a chat with the person you want to call. Then select the "Free Call" option. You need to have the free Facebook Messenger app installed, a Facebook account and be connected to Wi-Fi for the feature to work