WhatsApp is a cross-platform messaging app that allows users to exchange messages without SMS charges. It is available on iPhone, BlackBerry, Android, Windows Phone and Nokia and only requires an internet data plan. The app features include pictures, videos, voice messages, audio, user locations, and contact sharing. WhatsApp was launched in 2009 by Jan Koum and Brian Acton and has since become a worldwide messaging service, gaining popularity through word of mouth promotion and affordable pricing.