Any visitor to the United States gets used to being asked for their ZIP code, or being confronted with forms in which only an American address will fit. Normally there’s a way round it – after all, you don’t really need to be a US citizen to purchase groceries, fill up the tank of your car or register at a hotel.  You would also imagine you don’t need to be an American citizen to indulge in a little cellular data communications from your iPad – but you would be wrong.

I took my UK-bought iPad to the States last year. The folk at Apple UK advised me that none of the carriers had roaming packages in place. Even if they did, it would be much cheaper to buy a mini-SIM for the iPad in the USA from AT&T. At that time, AT&T had the monopoly.

The first stop on my quest was the Apple Store in New York. The orange-shirted dude at this cathedral of aspirant computing apologised that he could not sell me one – the only mini-SIMs they had were installed within the iPads on sale – and sent me down the road to the AT&T store.

As luck would have it, the A&T store had one – their last one. It was $30 plus tax. “Just put it in and then complete the sign-up online”, the assistant directed. “Choose a plan, enter your credit card details and you’re away.”

Being away was the very next problem I hit. Back at my friend’s place, I slipped in the SIM and started the sign-up process. The AT&T logo appeared and the company’s gnomic new strapline “Rethink Possible”. Then familiar US address – street, city, state and ZIP – scrolled into view. With drop-down for country and no check-box for “international”, the form made a 100% assumption that you were an American. Mindful that credit card companies are wont to stop your card if you enter a wilfully incorrect address, it was a case of Rethink Unavoidable.

Back at the AT&T store, after a very long wait, I got to speak to a customer service agent who told me there was no way I could do it unless I had a US address “for security reasons”. He was making it up. It was a large store, so I circled the displays and then approached another counter. This time, the assistant was more biddable and telephoned customer support, and after a very long wait, they advised that I buy a “prepaid credit card”. Such things do exist, I learned. They feature heavily in the twilight world of the uncreditworthy. They don’t sell them at AT&T: they sell them at drugstores. I lost interest – four hours on a fruitless pursuit was enough for one trip.

Now, on my next trip to the US, it was time to have another go. After all, it would be useful to get email and Google maps when on the road. A drugstore sold me a $50 prepaid VISA card for $54 plus tax. This was getting expensive too.

It was time to activate. The address where I was staying seemed to fit, and AT&T sent me a message to say “activation successful”. And then another one immediately to say “authorization failed”. I called AT&T’s 800 number, explained my problem, and got escalated – twice. Yes it was possible, but no-one could understand why it wasn’t working. Multiple ZIP codes were suggested for me to try. We even looked up the ZIP code of the drugstore, to no avail. “Success” it said, then moments later “failed”.

Eventually, in one very long period on hold, I checked the pre-pay card firm’s website to verify my card was still active. It was. I noticed there, you could optionally register your cards with – what else? – a US address. Any US address, it seemed. I entered the address in Phoenix where I was staying, tried again, and it worked. I even passed on this handy hint to the AT&T specialists, who were grateful for the advice. “That’s a new one on us” they said cheerily.

They also admitted they could see no reason why international credit cards could not be used – after all, I paid for the SIM with my UK Visa.  An unintended consequence or deliberate policy? We all blamed the tech team that designed the form. I was surfin’ and I’d broken no rules.

A final tip for the unwary – if you are visiting the USA, don’t buy a rechargeable pre-pay credit card. While that might seem more convenient than the disposable one I got, the registration process asks for something a bit more challenging – a social security number. Making one of those up is likely to get you deported.