While some pre-paid cell phone plans can be good, please read the details carefully. Many of the plans have minutes that expire if you don't use them. So if you buy a 60 minute "card" and toss the cell phone in the glove box for 90 days and then your wife has a flat and decides to call you to come change her tire, you might find out that the minutes you bought expired. Some had plans that expired 30 days after activation if they went unused. Some had plans that lasted longer, but it varied by the service provider.
My company sells goods and services to C-Stores, and one of the things we offer are phone cards, reactivation of prepaid phones, etc. You will find that prepaid cards work very well for some users, but generally they are expensive per minute, often 3 or 4 times the price per minute. If you don't use, or plan to use, a cell phone very much then they may be good for you, but they can off spottier service (depending on the provider) at a higher cost and they can expire (depending on the provided).
I am NOT saying they are bad, but I'm not recommending them to people who do not CAREFULLY look into them to make sure they fit your lifestyle.
AS FOR ALLTELL, you should check their coverage maps and make sure that they cover the area where your wife frequents. In rural areas many providers CLAIM to offer service but the CLAIM does NOT match REALITY.