Actually I'm surprised that it was Sony rather than Apple that came up with this idea.
Well, Apple certainly has come up with the idea even though they haven't yet realized it.
"Back-Side Interface for Hand-Held Devices"
An electronic device uses separate surfaces for input and output. One of the surfaces (e.g., the bottom) includes a force-sensitive touch-surface through which a user provides input (e.g., cursor manipulation and control element selection). On a second surface (e.g., the top), a display element is used to present information appropriate to the device's function (e.g., video information), one or more control elements and a cursor. The cursor is controlled through manipulation of the back-side touch-surface. The cursor identifies where on the back-side touch-surface the user's finger has made contact. When the cursor is positioned over the desired control element, the user selects or activates the function associated with the control element by applying pressure to the force-sensitive touch-surface with their finger. Accordingly, the electronic device may be operated with a single hand, wherein cursor movement and control element selection may be accomplished without lifting one's finger.
"Don't tell me I'm burning the candle at both ends -- tell me where to get more wax!!"