AT&T have announced an expansion of their pre-paid Mobile Share plans, offering relatively low-cost plans coupled with incredibly low data allotments. For US$20 a month you can get a whopping 300 MB of data each month, while $50 gets you 2 GB. Both plans include unlimited talk and texts.
Mobile Share plans create a bucket of data that can be shared among a number of different phones on one account. Account holders pay for the cost of their data along with a monthly charge for each phone activated on the account. Your price per phone goes down as you add more phones to your plan. So that $20 a month plan that looks like a crazy good deal is actually a $20 a month plus another $50 a month per smartphone.
This pricing structure has lead to criticism that the plans' advertised prices are misleading, leading some customers to overpay for less service. The Verge have put together an expose about the new payment plans being offered by AT&T, T-Mobile and Verizon. Before giving these new plans a shot, you might want to give their charts a look.