Facebook has begun rolling out its free voice calling feature to Facebook Messenger users in the United Kingdom, just days after the service landed in the U.K. on the iPhone. You won’t need to update the Facebook Messenger app; the feature will be added quietly in the background.

In an attempt to go head-to-head with the likes of iMessage and BBM in emerging markets, social network Facebook has just announced that it will be allowing users of its Messenger app to send messages at free or heavily discounted data rates.

WhatsApp, the hugely popular cross-platform messaging system available to Android and iOS, saw out 2012 with an incredible bang. The company has announced that it processed a staggering 18 billion messages on New Year’s Eve alone, exceeding its previous record of 10 billion messages processed last August.

WhatsApp could be the next item on Facebook’s shopping list.

Following its acquisition of Instagram earlier this year, Facebook is said to be eyeing up another popular service. Cross-platform messenger WhatsApp could be the next item on the social network’s shopping list as the company looks to extend its mobile presence, according to sources close to the matter.