AT&T today followed Verizon Wireless’ lead and unveiled new shared data plans. But unlike its competitor, moving to the plans will be optional.

Like Verizon's plans, AT&T's new offerings allow users to connect multiple devices to one bucket of data, with an additional per-device monthly connection fee.

However, AT&T said there are no changes to its current device upgrade policy, so customers eligible to upgrade are not required to switch plans.

That could be a major differentiator for AT&T, as Verizon currently requires customers to move to its shared plans when upgrading to a new subsidized device. Customers who pay the full, unsubsidized price for a new device can stay on Verizon’s old plans.

AT&T is calling its new plans "Mobile Share” plans, and like Verizon, it has set the maximum number of devices that can be connected to one bucket of data at 10. One of the 10 devices must be a smartphone. Each plan includes tethering and unlimited domestic calls and texts for smartphones and basic or quick messaging phones.

AT&T has built savings into the new plans that give discounts to customers for using more data. The larger the data bucket, the less the customer pays per gigabyte, with an additional reduction of the per-monthly fee for each smartphone added to the shared plan.

For instance, a 1 GB bucket of shared data costs $40 per month, while the connection fees for each additional smartphone on that plan run $45 per month. However, the monthly smartphone connection fee is just $30 per month on a 15 GB shared bucket of data costing $150. Connections for additional devices in the plan include: $30 for a feature phone or quick-messaging device, $20 for LaptopConnect cards and netbooks, and $10 for tablets and gaming devices.

AT&T's move to offer shared plans isn't that surprising. The carrier's CEO, Randall Stephenson, told investors at a conference recently that the new plans were on the way, noting that connecting more tablets was a major impetus for repackaging data.

When asked whether shared data plans would simply result in customers using the same amount of data, essentially eating up minutes that would otherwise be left over at the end of the typical month, for the same amount of revenue, Stephenson said that the implementation of tiered pricing is already helping ease that problem.

"What I am most focused on is not family plans, but how we're going to connect the next device," Stephenson said, referring to the smartphone as the "platform" from which consumers will begin to connect other devices, including tablets, PCs, and even connected cars.

Industry analyst Jeff Kagan said in email comments that he believes most customers will choose the new plans on their own over the next several quarters as they get used to the idea, while others will change right away.

"This is similar to [the] Verizon Wireless Share Everything Plan announced a few weeks ago," Kagan said, "but the Verizon plan has too many rules attached."

While AT&T is offering its new plans as additional option for customers, Verizon is aggressively migrating its base to Share Everything plans, requiring that new accounts and new users go with the shared plans.

"That has kicked Verizon in the stomach with the negative feedback," Kagan noted. "I think eventually Verizon Wireless will follow AT&T Mobility's lead on this, or they will simply lose the competitive battle."

T-Mobile has panned Verizon's shared data plans, calling them “costly, complicated and punitive.” T-Mobile’s plans are based on throttling, which is the practice of reducing a customer’s download speed once they have used a certain amount of data in any given month.

Verizon’s Share Everything plans are currently available, while AT&T said its new Mobile Share plans will be available sometime in late August.