
US Telcos (can't) help themselves.
Perhaps the American public's lack of interest in prepaid mobile is due to the cellular companies desire for monthly recurring revenue without feeling any obligation to provide customers with a service in return.
Typically, if prepaid minutes remain unused for 30 days after you paid for them, the telco keeps your money and gives you a big, fat nothing.
Contrast that with, for example, Virgin Mobile in the UK. Last month while visiting on business, I used the left-over time I had on a pre-paid SIM purchased over a year earlier at Tesco!
The North American telcos are slowly being dragged out of their self-imposed Cellular Stone Age but they still regard revenue from customers as a right rather than something to be earned.