
This is what I found, and it is really cool. http://www.scosche.com/1998-up-volkswag ... -interface It takes the place of the optional external 6 CD changer that my car didn't have anyhow. It plugs in to the back of the radio where the external CD changer's cable is.
To the radio, it is a CD player. You can control the iPod from the radio, or from the iPod. I don't have an iPhone, but I bet it will play the music from it. (I don't know about phone call audio; does it go through the radio speakers? Would be pretty cool if it did.) The iPod is also charging while it's connected.
You can also use a non-iPod device through it's 3.5mm aux input jack. I haven't tried it and probably won't, all I care about is the iPod.
The only part that's visible is the 5' long cable connecting it to the iPod.