Facebook has rolled out an update to its Messenger app for Android that will allow users of the social network to start free voice and video calls with friends over a Wi-Fi or data connection. The free calling service launched for US and Canadian iPhone users back in January, while Android users received the feature early last month but only in Canada -- and 22 other countries since then.

The rollout will happen gradually throughout the day and doesn’t require a manual update -- although you and your friends will need to have the latest  current version of Facebook's standalone Messenger or Home apps installed in order for the feature to work.

The feature is a bit buried within Facebook’s messaging clients. To initiate calls from Messenger you’ll need to tap the ‘i’ icon button to the top right on a conversation and then select Free Call from your friend’s contact card. If you're using the new Chat Heads app that arrived with Facebook Home, you'll need to tap the three dots next to a person's name to move the conversation to the Messenger app before you can make a call.

This is the latest in a series of moves aimed at gaining a stronger presence in people’s smartphones, including the launch of a new home screen for Android as well as a new chat client called Chat Heads that lets you keep a Facebook conversation going with chats overlaid on top of whatever screen or app you are at any particular time -- the feature isn’t as pervasive in iOS, however, where it’s limited to the Messenger client.

It's worth noting that Facebook has offered voice and video calling on its site since 2011 through a tie-up with Skype, but the new VoIP feature on mobiles isn’t built on that partnership.