First the facts:
Part Number:
Snap-In adapter for iPhone4 (6NR music + video): P/N 84.21-2 218 390-02
Get it from Tischer:
iPhone adapters from Tischer BMW
I was about to order the adapter for my car which has 6NR, but I don't know what I would really gain over the normal USB cable?
I tried out my iPhone connected via USB cable and I could do BMW Apps and Pandora without issues. The album art shows up on the iDrive for USB media and Pandora, I don't really use the iPhone for music.