In Wyoming, only two carriers really work, Verizon and Alltel. Tracphone does have a program, but go 5-10 minutes drive out of town, and you are roaming. Both programs have free nights and weekends available, even on the prepaids. Both programs have free calls phone to phone, in the same carrier. Verizon appears to be more, but Alltel gets you on the little things...calls to email charge, even if there is no message. If you buy a $100 refill on Verizon, it lasts a year, and they have usage plans that you only pay on the days you use the phone. However, use 'em in the evening, after hours, and that day is a usage day, even if you didn't use it during the day.
We've used prepaids for years...no monthly bills and you have to pay for your own phones, but dollar for dollar, no surprise costs. Can't beat them. Also Verizon won't roam in most places.