AT&T this morning followed its rival Verizon Wireless by announcing new shared data plans that move away from limits for individual phones and shift instead to a shared data pool that can be accessed by up to 10 devices.

One big difference from Verizon’s approach: AT&T is making its plans optional. New customers or those getting new phones aren’t required to use AT&T’s “Mobile Share” plans.

So should you make the switch? In short, get out your calculator. It depends on how much data you use, and how many devices are in your family. In some cases, the new plans are cheaper, in other cases they aren’t. The Associated Press has a good rundown exploring different scenarios on AT&T. Also see this AT&T infographic. Fierce Wireless compares the Verizon and AT&T plans.

In my case, for example, it looks like my family would save around $50 a month on our overall AT&T bill if we’re willing to give up our “unlimited” data plan and shift to the new Mobile Share plan. Suffice it to say this will be a topic of discussion around the dinner table tonight.

In addition to the cost of data, talking and texting, AT&T will charge a monthly fee per device: $20 for laptops and broadband sticks, $10 for tablets and gaming devices. The company is betting long term that people will add a wide variety of devices to their plans.

“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,” says AT&T exec David Christopher in a news release.

The new AT&T plans are set to launch in late August.

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