Or indeed one of these? http://www.ebay.co.uk/itm/BMW-Z4-2002-2008-Car-iPod-iPhone-5-Interface-with-Genuine-Lightning-Adaptor-/400516446142?_trksid=p2054897.l4275
It looks like the schosche works in the same way as the OEM kit, and doesn't allow you to control iTunes from the iPhone itself, only playing set playlists. It's quite frustrating and limiting in my experience.
Or you may want to try one of these, Just put one in myself, they are really plug & play. Non-dsp version is also available.
http://www.amazon.com/USASPEC-PA12-BMW-DSP-In-Vehicle-Interface-Adapter/dp/B0016AOO6Y