Granted, it is US-only right now, but Facebook offering free voice calls is big news - and should be in the UK before you know it.The system recently had a trial in Canada and is now rolling out across the US, with a UK launch likely to follow if all goes well. At which point, you should be able to make free calls via Facebook. Or at least, some of you will.First off, you'll need to be using the iPhone app for Facebook Messenger - as will the 'friend' who you want to speak to. Add to that a gradual rollout and even if you are in the US, you might find contacts are very limited. Hopefully the UK launch will be more immediate. If you find someone, nudge the 'free call' button and you can talk to them over Wi-Fi for free, rather than just tapping a message on your keyboard. When you are done, hit the 'end call' button and it's over. There are also speaker and mute buttons, plus a ring sound when you are trying to get through (not unlike Skype). It sounds useful, but how much you use it probably depends on how much you use Facebook for general communication. But it is free, as are the calls - and if you already use Messenger, there's not even any hassle of a new download.When we hear about a UK launch (and of course, an Android launch), we'll let you know.