Skype /ˈskaɪp/ is a telecommunications application software product that specializes in providing video chat and voice calls from computers, tablets, and mobile devices via the Internet to other devices or telephones/smartphones. Users can also send instant messages, exchange files and images, send video messages, and create conference calls. Skype is available to download onto computers running Microsoft Windows, Mac, or Linux, as well as Android, Blackberry, iOS, and Windows Phone smartphones and tablets. Much of the service is free, but users require Skype Credit or a subscription to call landline or mobile numbers. Skype is based on a freemium model.