Truphone has announced the first free telephone application for Facebook users. The Call Me application does not require a Truphone account, l nor a special phone, just a Facebook account. It works by enabling the user to choose a number on which they want to take inbound calls, and the Call Me button in their profile can then be used to make free calls.

But, as with all such things, you need to read beyond the marketing hype and headlines to reveal the devil hiding in the detail. Much is being made of this being a 'free' Facebook phone system, but actually the deal is that calls are free only until 'at least December 31st 2007' which is in line with the current Truphone pricing policy. What happens in 2008, which is only a matter of a few weeks away remember, is not clear.

Still, for now at least, it's an interesting and useful addition to the Facebook application armoury, which allows anyone to make a call directly from their PC by simply clicking on the Call Me button to initiate a Truphone softphone call. The softphone application is embedded into Facebook, but interestingly does not require both caller and callee to add their numbers to a directory list.

You could say it is click to call rather than click to call back in fact.

The fact that is can be set to only be visible to a user's friends, and that actual phone numbers are never revealed, helps the social networking friendliness.

Dean Elwood, a director at Truphone, told me that "The Truphone Call Me application is completely embedded within the existing Facebook user experience. We never make a user leave Facebook or have to pick up another device such as a phone; instead, we've embedded a softphone into Facebook. One particularly exciting thing is that anytime a new service that accepts attachments is introduced to Facebook, our application will work on it because the Truphone Call Me button can be dropped into any attachment. So people may use our application in ways that haven't been envisaged yet."

While Truphone CEO James Tagg adds "In the same way that messages on Facebook are always welcome because they are by definition always from friends, phone calls from friends are surely welcome too. We want to encourage people to talk to each other more and, using Truphone, we can help to get people talking again spontaneously and for free."

There's a YouTube clip of the Facebook phone in action here.