Skype developers should worry starting from now as it has new competition on the iPhone platform thanks to Viber, a new VoIP app that allows you to make unlimited free calls to other iPhone users over Wifi and 3G connections. The app is totally free, runs in the background without draining your battery, doesn’t have any ads and won’t charge you anything to make calls.

As you know that FaceTime is only available via WiFi, but now you can make FaceTime video calls with Tango. What does this application? Tango offers high-quality video calling between iPhones and Android devices including Droid, EVO, HTC Hero and NexusOne, and works on 3G, 4G, and Wi-Fi. It is now available for free on the App Store.