Up until a few weeks ago I was accustomed to playing music in my car
via my BlackBerry which interfaced with the stereo via a cassette tape
adapter. It was an acceptable enough solution right up until my tape
deck decided to crap out on me. I went mad without my music for a
week before deciding to take action. Since the existing deck is a
double DIN stock VW job, replacing the whole thing was going to be
crazy expensive and FM radio interfaces have never impressed me much.
Without many other options at hand, I looked around the web to see if
I could hack/mod/fix it myself. I ended up buying an interface
designed for XM satellite radios and attached it to the 12 pin interface
originally designed for adding a 6 disc CD changer. All I had to do
was remove the stereo, connect all the cabling, fish some wires, mount
the jack, and voila!
 
12 PIN XM Commander Interface: $65
Stereo Removal Tools: $20
RCA Stereo to Female 3.5mm: $34
 
Not bad, eh?