It was first seen in the US back in January, but now the UK's Facebook users can also take advantage of free calls via the company's Facebook Messenger app.Yes, free calls. That's as long as you have the Messenger app and a Wi-Fi/3G connection and the person you want to contact is also a user of Messenger. If that person doesn't have it open, you can leave a voice message, so they can pick it up later.But if you are both online, you can make those calls. Just connect via the button in the app, with options to end the call, mute or mute the microphone, as well as being able to return to the main app easily.The calling features are in beta right now, so you might encounter the odd glitch as you go, But nothing significant has been reported so far. Oh yes, it's iOS only right now, but we suspect an Android version should follow soon enough. If you have an iPhone and like the idea of it, go get the app (or load it up) now.