Android: Viber is a free app we've previously featured for making free calls from an iPhone over 3G and Wi-Fi. Now available for Android, you can call or text other Viber users (including iPhone users) for free.
Despite being completely free, Viber doesn't have any ads. It also doesn't require you to register or create an account (it uses your phone number as your identifier) or create buddy lists - it works just like a phone. A big plus of the app is the free international calling and the ability to use Wi-Fi to place calls.
All you'll need to make the most of the app is get more friends to use Viber, whether they're iPhone or Android users.
Viber [Android Market]