They may just ask you to pay a deposit of a certain amount of money to ensure that you're going to meet payments. I believe this would be refunded after the first 3 bill payments have gone through. I don't know if this happens with all cases but I know my friends have done it.
You get internal checks with expensive handsets. Mainly your billing will be checked to make sure you have up to date bills and pay on time. I think their may be problems also if for example you live in Glasgow and want a handset delivered to London.
Lets face it he is a straight up guy, he is still on a rolling paid monthly contract and he lives around newcastle. What more do you need.
Not really having fun, but as long as you are still on your contract and it's paid by DD don't think they will even do a credit check. It is possible depending on their systems that when they tried to process the upgrade the computer would hiccup! But getting bit personal that would depend on what happened 2 years ago!
Just go for it, probably no problems at all but if there are you can't sort them out till you know they are there.