USA customers, please provide me some info!

I have travelled to Mexico and South Africa and used prepaid SIM cards for travel at cheap rates. Is there prepaid SIM cards I can use for my blackberry in the USA? Anyone know what company offers this service? A week or two week service (BIS)?

thanks!

I believe Tmobile offers something. call them.

This is a site I suggested to a friend a few months back. USA SIM card