The invention is directed to a physical overlay that can be secured to a mobile device and that covers at least a portion of the mobile device's user interface. The overlay includes a front portion that has input areas, which may be openings or physical keys. The mobile device detects or is told that the overlay is installed, and the mobile device receives configuration data associated with the overly that tells the mobile device the locations of the input areas on the overlay so that the user interface can be adjusted accordingly. The overlay also includes side portions that allow the overlay to be secured to the mobile device.