Viber is an instant messaging and Voice over IP (VoIP) app for smartphones. In addition to instant messaging, users can exchange images, video and audio media messages. The client software is available for Apple iOS, Android, BlackBerry OS, Nokia Series 40, Symbian, Bada, Windows Phone, Mac OS, and Microsoft Windows. Viber works on both 3G/4G and Wi-Fi networks. It first requires installation on a phone in order to work on a desktop operating system environment.
WhatsApp Messenger is a cross-platform instant messaging client for smartphones. It uses the Internet to send text messages, images, video, user location and audio media messages to other users using standard cellular mobile numbers.