Viber is a free instant messaging and voice calling application for smartphones. It was developed by Viber Media and released in Dec 2010. It is compatible with Mac OS, Android, BlackBerry OS, iOS, Series 40, Symbian, Windows Phone and Microsoft Windows.
This program allows users to call other Viber users over the Internet, incurring only Internet data charges. Installation and registration is free and takes only a few minutes, as of 2014. Once installed on a smartphone, the software scans the user's contacts list to add the names to its list of Viber users.
Viber works through 3G and Wi-Fi connectivity. It also works on desktop computers but must first be installed on a smartphone. Viber has more than 280 million registered users, of which more than 100 million are active users.