[simonw]

When I visit the US from the UK I use T-Mobile pay-as-you-go SIM cards to get data on my iPhone. It works great - you go in to a T-Mobile store, pay for the SIM and $3/day of credit (I normally spend about $25), they set up the phone and profile for you and you walk out within a few minutes with a working iPhone.

I used to use AT&T GoPhone for this, until they sold me a "special deal for SXSW" in Austin that would keep my number and data working for multiple trips three years for $100. A few months later they cancelled the data portion of the plan (naturally refusing to refund my $100 since voice still works) and made it impossible to get pay-as-you-go data on an iPhone no matter how much money you give them.

They might have fixed that now, but they've lost me to T-Mobile.

[voltagex_]

I used T-Mobile too - the trick I wish I'd known about is it'll allow free (?) roaming on to AT&T in very select areas. Your non-US credit card may not work on the website either, I just preloaded the amount I needed while at the store.