There have been many unique patents by several manufacturers. Samsung has applied for a patent with the United States Patent Office that is labeled “MOBILE TERMINAL HAVING REAR KEYPAD”. That’s right… it will preform a sort of Inspector Gadget appearance of two half QWERTY keypads.
According to the description “A mobile terminal having a rear keypad is provided. The mobile terminal includes: a main body having a front surface and a rear surface opposite to the front surface; a touch screen disposed at the front surface of the main body; and a key input device having a keypad disposed at the rear surface of the main body and extendable outwards to sides of the touch screen”