GPRS is available in most populated areas and it's generally faster than in the UK I have found, but I don't know of any PAYG providers. PAYG is quite expensive in the States, not like in the UK where it can be a good deal. I'd not bother as there are loads of wireless access point in the States right now. Find the best provider for where you hang out and get a months pass. To give you an idea, TMobile Hotspot will cost around $40 + tax a month for a non contract for all their US locations. Probably a lot cheaper than any GPRS you will find.