Yes the shark fin is the antenna for BMW Assist. While it is somewhat similar to OnStar (GM product), it also lacks some of the most important functionality of OnStar. On the plus side, if you're in an accident, the system will notify authorities and give them location based on the GPS antenna in the fin. On the negative side, unlike OnStar, the system CANNOT be used to track the car in case of theft. That feature was the one reason I kept my OnStar contract going. After the first free year of BMW Assist runs out, I seriously doubt that I will renew the service. And on the 5 series, the shark fin also houses the antenna for Sirius satellite radio, as opposed to the added "mouse" looking antenna.