If your car has option code 387 or 389 (pre-wiring for communication system) and The hands-free communication/cellular phone kit was installed you're good to go. It doesn't sound like the kit's been installed though. You need to find out if you've got option codes 387 or 389. This can be found on a VMI. You're local dealer can check this for you.

MB no longer supplies phone parts for the old cars. A company called AutoKonnect bought up all the old stuff FWIW