SHIFT 1.1 Viber for free calls on the iPhone :

The application Viber, available free on the Appstore, skips of national or international calls for free with an iPhone VoIP via WiFi or 3G.

After installation, the application creates its list of contacts from the iPhone and indicates which states whether or not Viber. The caller is immediately available without having to register in advance, such as Skype.

Update to version 1.1 of 24/01/2011
The 1.1 update provides an indication of receipt. Call quality is also improved, as well as Bluetooth