jailbreak it you can use any network then my iphones on asda mobile (part of the vodaphone network) 50p per mb if on the internet all apps work as chuck says if they need internet access they will work.i mainly use mine if i'm in a free wi fi area,
Why do you need to jailbreak it and remove all the security protection? Just ask your provider to release it or take on a Pay as You Go option from your current provider.