I imagine it would be quite easy to connect your phone to your head unit, someone electrically minded would probably find this quite easy. Where as I got an E in GCSE electronics, I really wouldn't have a clue :|
I can just about manage 2 light bulbs soldered in a circuit, but I can do this either in parallel or series Genius!!!
All I can suggest is searching google to see if anything like this exists. I also believe there have been previous threads refering to this, not sure on the outcome of those either.
I know for the Sony Ericcson W800i Walkman phone u can buy a connection which is like the headphones but splits to phono leads. Just put that into the AUX and your laughin