Scared myself silly today when I finally installed the mobridge - when I started it up to see if it worked - NO MMI! Completely dead!
As the more astute of you may have already figured out, I had simply neglected to replace the fuse for the original 'phone module - which I drew the power from - meaning that the MOST corcuit was, of course, broken.
After replacing the fuse and cancelling all the ensuing fault codes in the VCDS - SUCCESS! No coding required - the iphone "just works" and music can either be played through a2dp (the interface is a bit clunky and long winded) or the provided ipod cable, which then shows up as another CD changer with playlists, artists, etc. as the disks.
Took a few goes to recalibrate the steering position sensor, which lost it's power too but now seems all good! Now all I have to do is remove the old handset from the armrest / build in the ipod cable and some form of cradle / route the mic cable up to the overhead lights.
Thanks to all for previous posts and assistance