Viber vs WhatsApp - Battle of the best free phone apps!
Viber and WhatsApp are both apps that aim to provide free communication between you and other smart phone users, without the hassle of manually adding contacts. This is achieved by identifying the users based on their phone number, so everyone in your phonebook that is already using the service will automaticly show up in the list of people you can contact for free!
A short summary of the features of the two apps.
Supports iOS, Android, Blackberry, Nokia/Symbian, and Windows Phone
Message popups (Android only)