At that point is it permissible to unlock it? That is really what I care about - for overseas travel.
Also, will buying through NEXT run a credit check? While I normally wouldn't care, I may be applying for a mortgage in the next six months or so, and would prefer to keep my credit report inquiries to a minimum.
Once it's paid off, AT&T will unlock it for you. Not sure about the credit check, but I would think if you're already an AT&T customer in good standing, there's no need for it.