According to BMW as shown in the link http://www.bimmerboard.com/forums/posts/451067

Just like the RAZR, they limit the iphone to the new body style BMWs and give this comment. Due to the broad dimensions of the Apple iPhone the Snap-In-Adapters in not supported in Vehicles of the model series X5 E53, X3 E83, Z4 E85/E86, 3 Series E46, 7 Series E38 and 5 Series E39.

Of course the Iphone still works perfectly with BMW bluetooth module 3th generation as found www.bimmernav.com but the snap in adapter seems to wide for the E53