AT&T Wireless Follows Verizon's Lead, Rolls Out Higher Priced Shared Data Plans
Starting next month, new and existing customers can choose one of the following tiers:

Source: AT&T
"Today we think of people’s smartphones and tablets sharing a bucket of data. But in the future we’ll see health care monitors, connected cars, security systems and other devices in the home all connected to the mobile Internet," said Christopher. "Our Mobile Share plans are simple, easy and a great value for individuals or families with multiple mobile Internet devices."

AT&T says it won't force customers to choose a shared data plan if they don't want to (unlike Verizon), and that's a good thing because you could end up paying more for less data. For example, on a non-shared plan, AT&T charges $30/month for 3GB of data, compared to just 1GB for $40/month, though there's some value in the unlimited talk and text portion.
Also included in the shared plans is access to more than 30,000 AT&T Wi-Fi hotspots, AT&T said.