How do I hook my iPhone up to my BMW 530xi?

So, I want some device or cable that can hook my iPhone 3G to my BMW. It has a navigation system, so the layout and functions will be a little different than a BMW without one. I'm not looking for an auxiliary cable, because I want something that will allow me to use the controls on my steering wheel to change the track and volume and stuff. If you could find something cheap and affordable that can take care of the job, that would be amazingly great!! Thank you so much!How do I hook my iPhone up to my BMW 530xi?If your car has a USB and aux input plug in the center console then you need a adapter cable part number 61120440812, its about $70 to $100 depending on where you buy it. That may be an old part number. You should just ask your dealer for an ipod interface cable. That is just a plug and play interface. If you don't have a USB port you will need to have it retrofired. This will need to be done at the dealer or a good independent shop that has the ability to program your vehicle. The cost for this will be $500 to $700 depending on labor rate and the markup on parts.