Apple has been granted patents for invisible buttons and slider controls that its been working on since 2006.
While the patent was granted on May 7th, it was actually filed nearly five years earlier - on Oct 24th 2008.
The patent details that the buttons would be made of the same material as the device’s housing, and set flush to the surface, indicating the buttons would appear as part of the iPhone or iPad bezel. “An input device includes a deflection based capacitive sensing input. Deflection of a metal fame of the input device causes a change in capacitance that is used to control a function of an electrical device. The input appears selectively visible because it is made of the same material as the housing it is contained in and because it is selectively backlit through tiny holes.”
It seems a backlight will illuminate the invisible button or slider's location when it is needed, with a sensor used to track the user's motion.
It is possibly too late for this tech to be included in the next iPhone, but we could be seeing it in the iPhone 6/6S/7/whatever.
Check out Apple’s ‘disappearing button and slider’ patent here.