Facebook Unveils free calls for US iPhone users. Calling all iPhone based Facebook users, the social network launched a feature within its Messenger app that gives iPhone owners the ability to call each other while connected either via Wi-Fi or their wireless provides data network.

This calling function makes Messenger into more than just an SMS or iMessage challengerCompared to a traditional cellphone call, voices sounded a more hollow and electronic, and we could hear a bit of background noise. Still, it's more than passable, as the caller could be heard clearly on both ends.

If this feature proves to be consistently stable and functional, Skype could have a real competitor on its hands, not to mention Google Voice. Wireless subscribers who aren't already signed up for an unlimited plan would also have the flexibility to opt for less voice minutes, knowing that more of their calls will be carried over data pipes.

Stay tuned for continuing coverage of Facebook's new features, including more hands-on testing and impressions.