And that makes it confusing.
The older cars require a lot of expensive hardware if you go OEM.
BMW will tell you its not possible in the US but people on this board have done it.
There are some aftermarket adapters such as the mobridge or Dension gateway 500.
Then there is this new one using a Euro Oem Hu that has USB , bluetooth and HD radio built in .
http://www.e90post.com/forums/showthread.php?t=687463
The first two require the cd changer option be enabled the last one also needs
programming as described in the link.