They also have SIM cards on sale.

http://www.straighttalk.com/wps/p…/shop/sims

Straight Talk AT&T GSM SIM Card (Standard, Micro, or Nano) $ 0.99
Straight Talk T-Mobile GSM SIM Card (Standard, Micro, or Nano) $ 0.99
Straight Talk CDMA SIM Card (Standard, Micro, or Nano) $ 0.99