https://www.newtis.info/tisv2/a/en/e39-530d-tou/repair-manuals/84-communication-systems/1usigiz

 

It's the TCU, Telematics Control Unit. Motorola/Everest version.
Known worldwide for premature failure across all BMW's of that date range/use.
Handles bluetooth and emergency call functions. Unfortunately that one unit (part number changed/was superseded some 20 times!) was changed and has more/less functionality depending on many option combinations of Nav, Homelink, sirius, and a whole host of others depending on what model car/radio/screen was available for the time/model/facelift etc.

If it worked(?) not likely and your phone's bluetooth paired with it, you'll loose that for sure. I'm unsure about the E46 but on some later models you would get a flash message of "SOS Call Not Enabled" on startup. Can be coded out.

On later cars with this same module, it was very often the culprit for the car having a draw/car NOT going to sleep.
On some models they conveniently mounted these standing up and/or in the spare tire well.
Up= water ingress through the pins on touring models.
Tire well = Let's go for a swim.
They sucked.

https://www.newtis.info/tisv2/a/en/...lecommunications/tcu-telematic-control-unit/tcu-supply/tcu-control-unit/YRzUklS

 

It is in fact a TCU with Assist. Here is a guide to the part numbers for that module:
http://www.bimmerboard.com/members/prof330i/original/BMW-TCUandULF-PartNumbers.pdf

I use a TCU for my in-car Bluetooth phone integration and it works perfectly. You lose BT when you remove it. BTW, the pairing code is 8943 if you want to test the bluetooth.