The fin is an antenna for more than one system, so there is more than one configuration that will result in the presence of a fin/antenna assembly. The "truth" here depends upon (a) when your car was made, and (b) which market it was produced for. We're starting to get our wires crossed a bit because we're comparing vehicles made for different markets. While the mechanical/drivetrain differences are generally slight, there are often significant differences in the baseline trim specification from one country to another.
BMW USA specified that all BL93 (US spec) M3s received telephone pre-wiring as a standard feature. (This was an extra cost option -- code 640 -- in most other markets.) Telephone pre-wiring did insure that all of the requisite wiring and connections were in place throughout the car, but did not involve the installation of other related components, such as the headliner microphone, telematics unit or fin/antenna.
When the 2003.5+ cars equipped with the Premium Package began rolling off of the line with BMW Assist, they got a couple of components added to the mix, including the microphone, rectangular mirror, telematics unit and fin/antenna. For this reason, the alternate inside mirror is a sure tip-off that the car was delivered with BMW Assist.
As we've seen elsewhere in the thread, satellite radio installations also terminate at this same antenna, which is why some cars that never were equipped with BMW Assist still got the shark fin/antenna. This is a less-common variation, obviously, but by no means impossible. It is also worth noting that a number of cosmetic retrofits were made on older cars once the newer models began appearing with fins, and these generally are not integrated with anything in the car.
Fin/antenna installations that are mated to the full telephone kit (which is similiar equipment-wise to the BMW Assist setup, but involves an entirely different telematics unit), may or may not be functional, depending upon whether or not a console-mounted charging cradle is present. Slipping a compatible phone into the cradle will create a hardwired connection between the phone and the fin/antenna; however, if you just leave the phone in your pocket and rely solely upon the Bluetooth connection to interface with the hands-free feature, you will not derive any benefit from the external antenna.
