Car-Mobile 9050

In my Audi there is an ex factory built-in car phone 9050.
Here is a bracket in which you can plug in the phone with a connection cord and a plug.
Question: Can you replace the plug with the holder for a telephone receiver with cable and plug connector?
The transmitter would have to work both with a real car phone and with a car phone.
I'd like a real car phone, because I already own a cell phone.