You most certainly can buy a pay-as-you-go SIM in the US. See http://amzn.to/wKySJq for example. The issue is complicated here however by the CDMA/GSM split, incompatible signal bands used by different carriers and not-truly-unlocked unlocked phones. Something like a million people in the US bought full-priced, unlocked iPhones to use on the lower cost T-Mobile netowkr but they don't get 3G bands. See http://blog.t-mobile.com/2011/09/26/about-the-iphone-a-lette...