Any prepaid data plan from any carrier?

[sjordi]

Hi,
I'll be in the US for the full September month and of course would love to be able to use the Internet functionalities from my European (unlocked) iPhone.

Problem is I don't want to be charged by my home country operator.
Is there any prepaid data plan available in the US (that uses a SIM card)?
I have a prepaid local number from T-Mobile, but they don't have data plans.

Any other carrier, including AT&T, offering a prepaid way to access data without commitment for more than 1 month?

Thanks for any help

[Quake97]

AT&T and T-Mobile are the only national GSM/W-CDMA carriers in the US.

Joe