Rebtel provides international calling apps for iPhone, Android, Windows Phone, and PC. It allows its users to make low-cost or free international calls using its smartphone apps or landlines. Rebtel works on any phone without installing software or an internet connection. The Company also provides an SDK allowing independent developers to integrate voice calling and instant messaging in their apps. The Rebtel SDK currently supports app-to-app communication over data, such as 3G or Wi-Fi and uses the same backend as Rebtel's own apps. Developers can decide how to handle user management, ringtones, calling screens and other aspects of the user experience. The Company as well develops Sendly, an app that lets users top up the prepaid mobile phones of friends and family abroad.