I had the same problem on my 04 745Li, which I bought used from a MB dealership. The local BMW dealership told me that I did not have the spacer card that rotated the phone ever so slightly toward the rear of the car. At the dealership I folded a business card and placed it between the phone and the front of the holder (toward the front of the car) and presto it worked and has worked since then.
Go know. I think BMW screwed up with their design of the phone holders and this was the fix that they came up with. It works.