I find it strange that if it is as simple as they make it sound, I would imagine we would already see this in play. My concern would be if this would be effected by outside lighting conditions.
I imagine this is something like a holographic touch screen thing where it pops off the phone. If so... D:
LED's can be used to detect light, including the detection of their own light reflected back into the LED. It would take a specialized display driver IC to read the reverse current flow, and you could probably scan an OLED display matrix it like you...