Just wanted to say thanks- This info was really helpful. I ordered the Part from Bimmerspecialist.com : part #82 11 0 153 367 - GENUINE MINI - and the install took like 30 minutes from start to finish. It was really straightforward and splicing the pins into the existing adaptor was incredibly easy.
$40 bucks and a half hour did the trick- now have iphone tunes in the Z4 and can talk through the phone when it is connected to the aux.
The only thing I did different was I used a stiff rubber cooking pan scraper to gently pull out the center vents once i used two small flathead screwdrivers to pull down the tabs.
This is the kind of scraper I used:
http://www.amazon.com/Progressive-In.../dp/B002BFHY4C
You probably have one in your kitchen.
thanks