A new update for the Facebook Messaging app for iOS devices now allows users to place voice calls to people in their friend list without using plan minutes (though you'll of course still consume cellular data). The company has been testing the functionality in Canada since early this month, and is now deploying the feature to U.S. users starting today. It's services like this one that will inevitably erode wireless carrier SMS and voice revenues, which is why AT&T and Verizon recently switched to shared data plans (read: they jacked up the price of data). Non cellular devices can use it too; any iPad or iPod Touch running iOS 4.3 or higher can now be used to make calls to Facebook friends.