[Bossman]

As other said, you do not have to be a UK resident to buy one. I have one myself. But, you do need a UK issued CC in order to be able to topup online with a CC. I believe you can just send an SMS, use GPRS, or make/receive a call to keep it active. I have not topped up mine in about a year, but I did log in to GPRS just to keep it active. It cost only about 35 p for a few KB of use. I did register my orange sim from here using my sister's UK address though. If you really need topup, you may want to check ebay. Every now and then you will see orange topups for sale. I bought a 20 pound topup on ebay for 17 pounds about 10 months ago.

I also know for a fact, that with both Vodafone and Virgin, you do need a UK issued credit card in order to be able to topup with one. Voda issues an error when you try to register a non-UK issued CC online. Virgin requires you to call in, and they will not allow it unless it's UK issued. I also bought a Virgin topup on ebay before my last trip. ONLY because it was cheaper that I would have paid in London. I paid 16 pounds for a 20 pound topup.