I've also been investigating Voice Control for my X3 (2006 model with latest ULF but no Voice Control option).

UK dealers cannot do retrofit coding of the ULF to active voice control as BMW has not, as of July 06, supplied a software component in the DIS to enable this particular retrofit. Note that no hardware is needed for more recent ULF's - you already have the microphone and Voice Recognition (SES?) software in the ULF as part of the BT system.

Now, a cinical view might be that since all necessary hardware and software is already in the car and a dealer price for simple retrofit coding is typically only 1 hour labour (£100+vat), word would quickly get out that the £225 option (520) could be obtained retrospectively for half price, hence damaging BMW new car revenue.

Ironically, could can purchase a retrofit BT kit from BMW with voice enabled. This is a standard BT kit including microphone and ULF etc that comes precoded with voice control active - see UK accessories guide. Parts price is £575 which is less than new car cost of BT and Voice options !