From what I understand and have been told, it is a limitation of the iPhone. The car is not built around a single phone, its built with capabilities that are usually more advanced than what a single phone offers. Blackberry phones have the most functionality as of now-until Apple hopefully gets on board and creates an update.
The thing is this: Apple unfortunately does not care about the small amount of people using iPhones in BMW vehicles, so they don't make it a priority to write software around our car.
The good news is that the car is capable....but only when the phone catches up!