You need the radio module (if in Europe: either Business RDS or Professional RDS). Only original BMW radio modules work, these sell for anything from 50 Euros to 300 Euros on ebay.de
There are old-gen (round pin) and new-gen (flat pin) radio modules, you need to have the matching wiring loom and radio nmodule, otherwise you cannot plug it in.

You also need the retro-fit wiring loom, as you car does not have the wiring for the video signals that go to the display, and does not have the wiring for the radio in the boot.


Look in the E46 navigation retro-fit instructions for the full circuit diagram.