I often wish people would read this before posting opinions about BT retrofitting as fact. I myself wasted hours researching this mostly because of misinformation.
http://www.e90post.com/forums/showthread.php?t=85149
That sticky is definitive.
The stearing wheel adapter + parrot kit is about $300+
The parrot is not an option with a 6 speaker system. Why? because it can only mute 4.
No vehicle integration whatsoever but the buttons. For that you need a MOST device.
There is one MOST device from Mobridge. The device is alluring -but- the car has to be programmed with a cd changer before installing it. If you don't have one you're SOL. If you do, you throw it away after install.
Ebay sellers do not do this kind of research before posting auctions.