Hot on the heels of Facebook's event announcing its new Social Graph feature, Facebook Messenger iOS app has been updated to VoIP audio calling functionality for US users. It's interesting since, technically, Facebook uses Skype backend, which is owned by parent company Microsoft. Thus, the collaborative user base is pretty vast. It appears that it is limited only to audio calls, but it is safe to assume that video calling is in the pipeline. VoIP may not use your monthly allotment of cell minutes but it will definitely use your mobile data plan, of course it will not effect your carrier plan if users use a WIFI acces point. The app is a free download available in the App Store.

What’s New in Version 2.1.1

• Back by popular request: Now you can swipe right to archive a conversation again
• Other improvements and bug fixes

*Free calling uses your existing data plan, and will be rolling out over the next few weeks.