An improvement to a cellular camera phone comprising a source of illumination positioned adjacent to the camera unit and configured to illuminate a portion of an underlying surface within the field of view the camera unit; programming effective to (a) collect a current tracking image frame, (b) compare the current tracking image frame with a prior tracking image frame, (c) compute a relative displacement between the tracking image frames, and (d) store the current tracking image frame as a prior tracking image frame; and a wireless peripheral interface, wherein the wireless peripheral interface communicates the relative displacement to a computer. Also, a method of retrofitting a cellular camera phone to provide wireless mouse functionality comprising the steps of providing an accessory unit for engagement with the cellular phone configured to position a source of illumination adjacent to the camera unit and to illuminate a portion of an underlying surface within the field of view the camera unit; providing the aforedescribed programming, and providing programming to communicate the relative displacement to a computer.