As with the leading carriers, there are periods when the prepaid players offer deals. Boost Mobile used to run a promo for new customers that let you get three lines with unlimited talk, text and data for $90 per month ($30 per line) after "your first payment of $100." It has since added a new unlimited plan that is $25 per month for new users, though each line must be separate and cannot be grouped on a family plan.

Boost Mobile has a few enticing plans at 5GB or less, particularly if you're a new customer. The carrier offers a $14 a month plan that offers 5GB of high-speed data per month with the ability to use that allotment for mobile hotspot. You'll need to prepay for 12 months of service to get this offer ($168), but it's better bang for your buck than the $15 per month for 5GB of data Mint Mobile offers new customers who prepay for a year.

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.

As I noted when covering the best unlimited plans, to get the most out of your deal you need to make sure you have the coverage you need. This makes it hard to give a blanket recommendation of any one carrier: T-Mobile's service in New York may be excellent, but if you're in, say, rural Iowa, Verizon is more reliable.