According to CNET, devices could be improved by concealing the buttons that would only become visible when needed.
These controls would become visible only when they are illuminated with the use of light sources.
The motion of the user’s finger or heat or sound detection could also activate the function.
The button and the smartphone’s casing would be made of the same material.
A slider control that would be mostly invisible, except when it is activated, could be used when browsing pages and documents.
Since production for the iPhone 5S is set to begin next month, the feature is likely to be implemented in the iPhone 6 or beyond.
Via Patently Apple