Viber is an Android* and iPhone application that lets you make free phone calls and send free text messages to other users that have Viber installed.
When you use Viber, your phone calls to any other Viber user are free, and the sound quality is much better than a regular call.
You can call any Viber user, anywhere in the world, for free and now also text them.
All Viber features are 100% FREE and do not require any additional “in application” purchase.

When you install Viber on your phone, it will scan your contacts and let you know who else is using the service so that you can call them for free.
Also, you can make it your default dialing application, so when you call a contact on your phone, it will automatically go through Viber if they have the service enabled too.