You need a Dice MediaBridge + Bluetooth module ($45) + DSP module ($90). It will set you back $360 shipped.
DICE MediaBridge BMW iPod / iPhone / Satellite / Bluetooth / USB Integration Kit | BSW
You also have the option of adding all the factory OEM bluetooth components, something to the tune of $700+.
I only know all this because I was interested in adding this to my '02 w/ DSP.
-Cyrus