Mitsubishi Phone in 1989 928 GT?

My recently-acquired 1989 GT came equipped with a Mitsubishi car phone and attendant antenna, as shown in the attached photos. I was suggested to me that the phone may have been factory-installed as option by Porsche. Does anyone have any information about this? It comes with its own separate charger unit, and I am wondering if it is contributing to the draw-down of the battery when the ignition is turned off. I am thinking of removing the phone
Dave