Viber is an app which lets you make free phone calls to anyone that also has the application installed. With Viber, calls and text messages to any other Viber user are free, and the sound quality is much better than a regular call. You can call or text any Viber user, anywhere in the world, as long as you have a 3G or WiFi internet connection.
Viber lets you connect with friends whose numbers you already have in the contact list. It synchronizes with your mobile phone number and contact list to instantly show who already has Viber. No need to create new usernames or build new lists.
Note: Voice calling is not available in beta, but it will be present in the final version.
· Windows Phone 7.5