As I understand it, the big thing with Mobile Application Preparation is integration with the iPhone BMW 'Connected' app which is supposed to give you:
- ECO PRO driving style analyser (requires the 'new' Pro nav unit).
- Wiki local search - what's nearby.
- News/RSS feed reader.
- Stream internet radio through the car (uses your phone's data plan?).
- Calendar on your phone can be displayed/read in the car.
- Twitter/Facebook posts are read out to you, plus I think the car can be set to automatically send its location.
- Last mile navigation - if you have to complete your journey on foot that could be handy.
- Vehicle finder (although the BMW Remote app can do that too).
- Enhanced iDrive interface when playing music from a supported iOS device.
The £600 retrofit price is from a 3rd party, and as I'd only be interested in the calendar and navigation bits, that's a bit steep for something that's a £130 option. I've yet to find out from my local dealer what it is though... although while BMW say it's available as a retrofit, dealer will probably shrug their shoulders