Tyler White's recent post on the Lawyerist blog gives good advice on cell bill savings. He went with a carrier that charges him only for what he actually uses.
He points out that switching to a budget cell carrier means paying full price for a phone. The contract-based subsidiy you get with a premium carrier will be gone. However, what you save in monthly charges should more than compensate you for the price of the phone. You need to consider how much data you use, the geographic coverage offered by lost cost carriers, and the cost of buying a phone that will work with your budget carrier of choice.
One of the discount carriers White mentions is Ting. Although I have my main cell phone on a Verizon shared plan because my wife, a public employee, gets a decent discount, I have a backup phone on the Ting network. Ting uses the Sprint network with Verizon as the backup for voice and text (data is Sprint only). Sprint coverage is not great where I live, but works better when I travel for my appellate practice (which is when I am most likely to need my backup phone). What I like about Ting is that I can "suspend" my service when not need, then unsuspend it when I travel. When suspended, I pay only $6 per month to keep my account active. When using my Ting phone (I have a Moto G), voice, text, and data rates are reasonable.