OK the part number the iphone 4 basic snap in adapter is 84 21 2199 389
I bought from amazon as BMW sell direct from there.
The link to see the part can be found here
http://www.amazon.co.uk/s/ref=nb_sb_...nap+in+adapter
The basic one just charges up the phone and connects to the outside aerial
The music one allows you play music from the device as well - as I use a USB stick for that, I saw that unnecessary and saved some money by not ordering that version.
hope that helps