This is the Software Publisher's description.
Viber is an application for iPhone that lets you make free phone calls and send text messages to anyone who also has the application installed. You can call or text any Viber user anywhere in the world for free.
Viber integrates seamlessly with your existing address book, has great sound quality and, once activated, does not require a PIN, username or any additional "in application" purchase. All Viber features are 100% FREE.