The app was created in 2009 by former Yahoo! employees Brian Acton and Jan Koum. WhatsApp allows you to send text messages, audio, and video to others - as long as you subscribe. But as long as you have a strong internet connection, the app will never add additional roaming charges to your phone.
Apps like WeChat and LINE pose a big threat to WhatsApp since they have the same features and are acquiring similarly massive userbases overseas.
WhatsApp is available for iPhone, Android, Blackberry, Nokia and Windows. Are you interested in WhatsApp?