Go back to your telephone/computer equipment room and look for some piece of equipment that has "Comdial" on it. I have quite a few of those phones that are supported by Comdial DSU II systems---a grey steel oblong box (cabinet) approximately 2 ft wide by 3.5 ft long and 3 or 4 inches deep--should be hanging on the wall. Google DSU II. These phones are also supported by other Comdial systems, however. Google Comdial FX II.