iPod/USB Adapter Parts List e90
These are the part numbers for post-March 2007 E90s with the 6FL option:
84109123739 USB hub
84109123739 Protective socket for USB hub (looks like the bottom of a container that the hub fits into)
84109125680 Cover for protective socket (the lid of the container)
84109143446 Adapter lead
61319129652 Aux-In + USB socket (goes in the center console)
I have no idea where the USB hub goes, I can't see it in my M3 that has the 6FL option. It is not under the trunk floor as far as I can tell.
I couldn't find any wiring variations apart from the adapter lead mentioned above (which looks to be short) so it seems probable to me that post 3/07 cars are pre-wired. I have no idea about coding either.
Obviously a "Y" adapter cable is also needed to run an iPod.
For cars between 3/07 and 9/07 without voice control and navigation an additional part is required, 84109149843.