One of the nation's biggest wireless carriers is rolling out a series of new data plans that change what's been a key part of the company's business for years.

Starting Sunday, AT&T will begin offering what it calls the Mobile Share Advantage plan, which eliminates the pricey fees that consumers currently face if they go over their monthly data allotment. Instead of a financial penalty, customers who blow past their data caps under the new plans will be subject to much slower download speeds — 128 Kbps, or a fraction of what users have grown accustomed to in an era of ultrafast data.

It's an approach that's been taken previously by the likes of T-Mobile, and could help ease the anxiety many people feel about using too much data. In addition, AT&T said Wednesday that it will be changing what it charges for data. It's adding more options for people who use a moderate amount of data, adding price points for buckets of 3 GB, 6 GB and 10 GB. Compare that to today, where midrange consumers can choose only among 2 GB, 5 GB and 15 GB plans.

But the added choice comes with a tradeoff: With some of the new data buckets, you'll be paying more compared to AT&T's current options. For example, whereas $30 will get you 2 GB of data today, it'll only buy you 1 GB under Mobile Share Advantage. AT&T is clearly trying to push people to buy bigger data plans, where the cost-per-gigabyte comes down the higher you go. Check out the new price structure in the screenshot to the right.