'87 325is

Has anyone had a shop do the work to wire your radio and install a phone jack or the like so you can plug in and play from the car speakers an ipod or mp3 player? There was a Roundel article detailing how to do this about a year or so ago.

Any place to recommend getting this done, either independent shop in the DC/ Baltimore area, or national chain?

Does anyone know where I can locate these or similar instructions electronically?