Fitted one to my 2005 passat recently which already had a rear roof mounted aerial, to be honest i wish i never bothered as reception is ok but not brilliant on the ones i actually like listening too (planet rock) in my area.
Not difficult as the aerial was close to the back and i only had to partially pull the headlining down, i managed to pull the cables through the roof lining to the front using a small plastic plumbing pipe fed through first.
Some trim and glovebox removal required but just take yout time, i chose to fit a powered one so a 12 volt supply cable was needed too.
I used one of these and reception is pretty good on the stronger stations such as absolute radio in my area.
Some of the other stations are pretty much unlistenable so double check reception in your area, its a bit hit and miss in cars to be honest.
You may be better off trying a bluetooth connection from your phone to stereo for internet radio.