Strange and hypothetical thought: could Bill purchase a US or international model of the iPhone with US or international iCloud account capable of ADP to activate ADP? Would this allow somebody living or working in the UK the ability to use ADP?
Only disadvantage that you will need to pay fot services via US gift cards as you need US bank cards otherwise.
AFAIK you cant just assign non-US bank card to a billing on US Apple account. At least it was the case before and at least for purpose of switching account region.
Thus you use USD gift cards since they easy to buy.