Got as far as entering billing shipping info. I assume this is my UK info and that later on I set an address somewhere to the US Unlocked address? Wasn't exactly sure though! Thanks's all
After you've hade the purchase at BFPS, they send you a card number, a CVV number, an expiry date and a website URL. You go to the website, put in the card details, then enter your address for the AVS (the US address). So, for buying at BFPS, you can just use your real address.