Earlier this month word got out that Facebook was trialing a free calling feature in Canada. We said that if those tests went well the company would expand to the US. Well, things must have gone swimmingly since just two weeks later American customers are starting to see the same feature turn up in the Messenger app. Just tap the "i" icon in the top right hand corner while viewing a conversation with a person and you'll see a button for a "free call." The voice