sim card for GPRS shield in USA

I've got a GPRS/GSM shield that I'd like to use, but I don't know where to get a SIM card for it. I'd like to get a pre-paid one instead of signing some kind of agreement with a carrier, but is that possible? It seems like lots of people are successfully using GPRS/GSM shields but I can't find any mention of what type of sim card or carrier people are using here in the US.

Does anybody have a SIM provider suggestion?

You can buy a cheap verizon flip phone with sim chip for about $20 at Wal-mart or some gas stations.

Verizon phones operate on CDMA, which is different hardware than the GSM/GPRS module I want to use. So a Verizon SIM card is useless. Any other ideas?

I went with these guys http://www.gprssim.com/index.php?route=common/home
$5/month for 500k and $10 for the SIM card.

$5 per month was what hooked me for development I am not worried about the 500k limit, if I need more I may look around a little bit more. I just ordered the SIM so I do not have much idea about their service ask me in a bit.

Thanks
wade

Wade I'm wondering how you like the service?

George