There's a new VoIP mobile application in town, to challenge the likes of Skype, Fring, TruPhone et al. And the good news is that it's out on both iPhone and Android.

It's a free download to your handset, and rather than relying on building a community of contacts in the way that Skype does, it automatically taps into the largest appropriate social network that you already own - your Facebook friends.

Calls are made over either Wi-Fi or 3G, if you're out and about, and so to all intents and purposes are "free" provided your data plan is adequate, of course. The app still requires the people you call to have the Vonage software installed as well, but that's the only barrier. Beyond that, you don't need to know their phone number or have it in you contacts book at all. Just hit the talk button and the call will connect so long as they have some kind of data connection going on at their end too. If your contacts haven't installed the app themselves, you can still message them.

The service will work for calls worldwide, but remember that you'll still be paying for roaming data if you happen to be calling or receiving in a country where you don't live and are using 3G rather than Wi-Fi.

The launch might be of most interest to Android users who have so far been left without a Skype app, as the added advantage is that once you've started up the Vonage program once, it's always on in the background from start up. All notifications are also push as well, so you'll know about it when someone's trying to get hold of you.

While this is the company's first foray into the mobile space, Vonage has a strong user base in fixed line VoIP in North America and there's big plans to take this service to other social networks as well - with the likes of LinkedIn and Twitter also mooted - provided a blocking system is introduced further along which might help prevent unwanted calls.

"We don't see this so much as a move into mobile", said the Vonage CEO. "The future for us is more about being able to make and receive calls irrespective of what devices people are using to do so".

Of course, in order to accomplish that, there might also be the need to create a desktop application and also add extras such as conference and video calling to the party as well. Should this first launch prove successful, the fact that Apple's FaceTime is restricted to iPhone users might not be an issue any more.

So, what are your thoughts on the matter? About time there was good VoIP on Android for 3G or is this just another internet calling app to be lost in a sea of others? Let us know in the comments.