After buying a shitting 3gs this week i fucking want the new one

Cant use the 3gs on o2 as its vodafone and i dont want to jailbreak.

So if i buy the phone from apple can i just go to o2 and get my sim changed to the micro one? Fucking o2 aren't selling them on no contract yet.

tesco have them for £479 pay and go. So are these fuckers locked also?