Scousus, not sure if you could convert the old ipod ones to USB as they were firewire charging which is a different voltage and pin out you would need to track down a converter. Alternatively if you got one of the cubby hole trims they have a seperate section in the lowere plastic where you can get aircon vent in to cool or heat the box, I reckon that could be easily converted to a cigarette 12v unit with a USB cigarette plug in for charging phones.
Peter, I believe the MDI is only compatible with the third generation stereos so you would need an RNS510 RNS310 or RCD510 or equivalent to operate the MDI interface.
The one at the start of this thread works with the older units and acts and uses the CD changer cabling and will play the first 99 or so tracks and I dont believe it will give you track names just numbers. I believe it was an Audi unit but im not 100% on that.