As of February 2015, WhatsApp functions only on certain smartphones. Attempts to download the application on an unsupported device generate a message informing the user that the device is not supported.
WhatsApp Messenger is a messaging application that can be used in lieu of or in addition to the short message service, SMS, provided by cellular phone carriers. The application uses the data service provided by smartphones to send and receive text, voice, picture and video messages. The service uses encryption for all data sent between the user's device and the company's servers. WhatsApp is free during the first year of use, after which a $0.99 per year fee is assessed.