Not wanting to put a damper on folks enthusiasm for this, I did find this post on e90post where a guy had a USA built E90, and ordered the Retrofit camera kit ..... its a old post, so need to bear that in mind.
http://www.e90post.com/forums/showth...+camera&page=4
BMW rear view camera retrofit problems
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Greetings,
I may be the first tester of the BMW rear view camera retrofit. I currently work in Germany; my car is a US-specs 2006 330i with idrive and the nav. I ordered the camera retrofit, which was supposed to work on my car according to BMW specs (was listed on the dealer's list). The dealer installed the camera and the converter box (all supplied by BMW), tried for three days to make it work, including several calls to Munich but to no avail. If the camera retrofit worked (although the image was not using the full width of the navigation screen), the rest of the car's idrive system would shut down. After three days of trying to sort it out with BMW, BMW support in Munich told the dealer to send it back for them to investigate further. The dealer pulled the camera out and sent it back to Munich. End of story.
Bottom line: retrofits are always tricky business. I had a similar experience back in the States with my previous 3 series (E46) with the BMW bluetooth retrofit that also didn't work as advertised.
I hope my experience will help others who contemplate retrofitting the BMW camera."