Have you tried giving your home address just to see if it kicks it?

I'll never understand why they just don't link up the 3G service to a customers att account...

After some looking around at the relevant Apple forum, it appears that there is a federal law that requires any wireless service to be associated with a physical address.

It's the Mobile Telecommunications Sourcing Act. Here's a link but I don't recommend wasting mental resources on it. All the law requires is a physical location be listed, not that the provider bill to that address. AT&T is just being lazy.

Here's what AT&T says: https://www.wireless.att.com/cell-phone-service/checkout/cannotBePOBox.jsp

I understand that issue. That's why sometimes when I'm making a purchase online the vendor wants a physical address. But legal requirement is not for the billing address, as you say, and AT&T provides absolutely no workaround whatsoever except for me to change my billing address with my card issuer.

I've never in my life been forced to do that simply to make a purchase.

(FYI, in my Day Jobbe I work somewhat with transaction processing and with fraud detection/prevention, so this stuff all does make sense to me. And they're doing it *wrong*.)

No, PO Boxes generally have their own separate zip code.

My phyiscal zip is 97222, my PO zip is 97242.

Hmmm - I wonder if a pre-paid debit card associated with your street address would suffice to set it up, then change it to your standard credit card?

To get around this, I've had some success with registering a second address with the credit card company and giving that address only when it's needed.

For some reason, the Verizon tower in my neighborhood is flaky. Some times I would get signal in the house, sometimes not. I complained, it did no good. So I went to AT&T and haven't had a problem since.
Meanwhile, it is 10 years later and my friends still complain, some times they have problems getting a signal in my neighborhood.
Note- We are right next to a Major Highway, we suspect Verizon set up their tower for the highway and the neighborhood has to be happy with the overflow signal. So if there are too many cars using Verizon on the Highway, we lose signal and have our calls dropped, again.
AT&T is always 5 bars for me, anywhere in the house.
So yes, AT&T is annoying as hell, but at least I don't have my calls dropped on me.
And I too have a PO Box which I prefer for my official mail address. The family also has several credit cards, two of them "use" the street address. Since I have all the bills and legal notices for all the credit cards e-mailed to me, the address of record is mostly for those times when someone needs a street address associated with a credit card, I give them one of those two. Beats arguing with stoopid systems.

How quickly does your card issuer process billing address changes? (switch it to your street address and then switch it back after ATT bills it? They shouldn't query that information after the first transaction anyway)

Do you know if it has to be a street address in the USA?

Reason: I do enough travel to the USA that I would like an AT&T micro-sim for my iPad 3G (when it materializes -- they're not on order outside the USA for another nine days, dammit, and won't ship until the end of May).

It appears to not only be a US street address, but also a zip code that is inside the AT&T 3G coverage areas.

Which is really really stupid. There's a huge potential market of regular US visitors who would buy one just for the 3G connectivity...

Hey there, Dave works for At&T, and he's far from being an idiot. Please don't lump policy and individuals together on this!
I know you don't blame him personally, still it's a kick in the arse.