Viber is a new free VoIP app for the iPhone. It allows you to talk using the AT&T data network, rather than the cellular network. I kept looking for a catch, but there isn't one. Works on WiFi and 3G. Check. You don't need to create a friends list. Check. Alerts you to incoming calls without the app being open. Check. No ads. Check.
International and domestic calls between 2 Viber equipped iPhones are free. You aren't burning your voice plan minutes, and soon there will be Android and Blackberry versions. Of course, if you have a metered data plan, you may have to watch out to make sure you don't exceed the limit, but many long-time iPhone users are still hanging on to their unlimited data contracts.
