1999 Mercedes C230 Kompressor RJ45 connection
 

There is an RJ45 Jack in my center console, ss the RJ45 connected to the telephone circuit?

If it is part of the circuit and I connected a bluetooth dongle to the rj45 jack...would it work? Would I be able to use my cell phone thought the telephone portion of the radio?

Pretty sure that connected to the phone cradle. Without all the other supporting hardware I don't think it would do anything. Further complicated that the car has the fiber optics connections.
Might want to ask in a different forum though