[Advice 1.1.4(1.1.2)]iphone with BMW

for thos who have a BMW the idrive in the car automatically syncs with your phone via bluetooth then it downloads your contact to the car screen to enable voice command over the phone during driving. when i had a nokia i never had a problem but witht the iphone i pair the telephone for the first time with the car for authorization then everytime i switch off the car and go out the next time i get in the car cant recognize the phone as the default phone of the car. this is not the case with all the other cell phone. can anyone help?