I will be visiting the USA for a couple of weeks in late summer. I am now looking for a pay-as-you-go (a.k.a. "prepaid") SIM card that offers me a certain amount of data that I can use. I am guessing that I will use up to 500 MB over the air. Do you have any suggestions about a reliable PAYG data plan? Where could I find more information? The AT&T and Sprint websites are a real horror to navigate through.