There are two main types of ways to pay for phone service: postpaid, where you pay at the end of the month, and prepaid, where you buy service before you use your phone. The advertisements you see for AT&T, T-Mobile and Verizon are almost always for postpaid plans, while the plans and carriers we're talking about here are all prepaid plans.  You're buying the data and access in advance of using it. Prepaid plan providers let you purchase in various increments -- 30 days, 60 days, 90 days, six months or even a full year -- with prices often varying depending on how long you're willing to commit.  In this story, I'm comparing single-year prepaid cellphone plans.