I'm pretty sure that the unlocked 8GB Pre you can order from Expansys is imported from Germany. If that's the case it will be unlocked but have a QUERTZ German keyboard (with the Y and Z keys swapped compared to the O2 UK version). You can certainly use a Vodafone UK SIM in one of those if you don't mind the keyboard. Alternatively you can buy a UK Pre locked to O2 and you can unlock it for £10 which will enable you to use it with any SIM. The website for unlocking is
here.