bmwfourlife, I have iphone 4s aswell, only had the car for less than 24 hours but have made 2 calls via bluetooth handsfree, both times I asked about sound-quality and both recipients said it was great. One call was made on highway even.
haven't noticed any real problems so far, no rattle, feels solid.
only "issues" so far is headlights got some fog in them, might go away, we'll see. Also the bmw-live feature is not working. I seem to be the only person in the world who ticked that option so don't know if more ppl got problem with that? I'm confident bmw will help out fixing that..
also noticed one minor "bug" in the idrive, when I go to the settings for the lightning at the floor where you can choose to have red or white color... I'm pretty sure that "classic" is supposed to be white color while "sport" = red lightning. It's the other way round on mine atleast, not that it matters =)