WhatsApp Messenger is a cross-platform smartphone messenger that works under iPhone, Android, Symbian, BlackBerry and Windows Phone systems. Easy instant messaging between users of different phone systems and international carriers is one of WhatsApp Messenger's main features. With an easy-to-use interface, users can also create a group conversation with several contacts. If you are away, the application records your offline messages so that you can read them later on. In addition, users are also able to send and receive multimedia files, including videos, images, and even voice notes. Since the app operates like an SMS exchange and uses phone numbers integrated from the user's address book, it requires neither pins nor usernames. The application also allows users to block contacts, share their locations, keep track of e-mail histories, personalize notification sounds, and many other features.