WhatsApp Messenger is a proprietary, cross-platform instant messaging application for smartphones. In addition to text messaging, users can send each other images, video, and audio media messages. The client software is available for: Android; BlackBerry OS, BlackBerry 10, iOS; Series 40, Symbian (S60); and, Windows Phone. The company by the same name was founded in 2009 by Brian Acton and Jan Koum, both veterans of Yahoo! and is based in Santa Clara, California.