Cell Phone Plans
Cell phone service in the USA has been dominated by four large players with partial monopolies and long contracts. This resulted in substantially higher costs than more developed (aka real) markets like Europe. This has recently been changing substantially and US cellular networks were forced to open up bandwidth to third party players. This means that you were over paying for cell service and can now do something about it. There are a number of players each catering to different usage scenarios, geographic areas, and network standards. It might be a bit confusing but a little shopping will pay off.
Mr. Money Mustache operates a lifestyle/finance blog devoted to cutting costs with minimal sacrifice. The author has recommended Airvoice, Republic Wireless, and Ting.
This is a massive guide to cutting as much from your communication budget as possible. Daley lists a number of providers with recommendations for different uses as well as general strategy for choosing. It is interesting to note that he dislikes Republic Wireless due to it's information privacy policies and hefty overage penalties.
A small selection of cell phone service providers
Note that while all of these providers will sell you a phone it is almost always cheaper to buy your own (including used Republic wireless phones on Ebay). The network standard used is also important if you plan on using your phone in other countries. CMDA is Sprint/Verizon and is pretty much only used in the USA. GSM is T-mobile/AT&T and can be found all over the world.
Republic Wireless uses a combination of WIFI and Sprints cell network (CMDA standard) to make calls. It can be cheap relative to other carriers depending on use scenario. However Republic requires the use of proprietary software and thus has a limited selection of devices available.
Airvoice is a fairly painless pay as you go provider operating on ATT's network (GSM standard).
Ting operates on the Sprint network (CMDA standard) and has a very interesting bin payment system. The idea is that you use what you need to and then only get charged for what you use.
Lycamobile is a massive global telecom making inroads into the US market. The plans are especially interesting if you need to make international calls. They are currently operating on T-Mobiles network (GSM standard)