AT&T has been under pressure from upstart wireless company T-Mobile for the past year and has had to respond on several occasions -- not always in the most graceful way. Now AT&T is showing it can not only respond to T-Mobile, but put pressure on the industry with its newly announced Mobile Share restructuring.

AT&T's new offer is designed to pull customers -- especially family units -- away from other wireless companies, as well as to get customers out of their subsidy system, which AT&T's CEO flat-out said was not a sustainable model for the future of wireless. And it's offering pretty deep price cuts to attain the double-sided goal.

Basically, AT&T's new Mobile Share plan offers as little as $15 per month per line, after a $100 fee for 10GB of data and unlimited talk and text, which the whole family shares. That means that for a four-person family, you'd pay $160 per month for four smartphones and a decent amount of data. Larger amounts of shared data of course cost more, but the cost per GB goes down as the amount of data per month goes up.

The $15 per line (per month) charge structure is much lower than traditional subsidized contract phones, which cost $40 per month, or even off-contract monthlies of $25. But the devil is in the details.

First off, the new Mobile Share pricing from AT&T is great if you already own an unlocked smartphone (or a bunch of them for your family). As I've mentioned before, the future of wireless is unlocked, and there are a number of low-cost unlocked (Android) smartphones that hit the market recently, with more undoubtedly to come, like the Moto G, Nexus 5, or any number of devices from smaller manufacturers. If you own unlocked phones, besides being able to jump from non-contract carrier to carrier, you can take advantage of deals like AT&T's.

But if you don't own an unlocked smartphone, there are extra charges. AT&T is pushing its Next early-upgrade program, which would typically cost about $20 for device charges, but deciding any non-contract phone, early upgrade or not, will bring up the monthly device charges in different ways. Here's a brief look at the cost structure with different options.

There's still a $100 credit from AT&T for new and existing customers who activate a new line of service, and compared to other similar wireless monthly plans, AT&T's now looks competitive.

Interestingly, AT&T went after Verizon with its announcement of the Mobile Share plan. Partly that may be due to the fact that in the monthly rate comparison, AT&T stacks up best against its chief competitor: T-Mobile is still a better deal for only two lines, and its growth since it began announcing uncarrier plans and incentives will probably continue to encourage the pink-clad market disruptor to disrupt some more. Or perhaps AT&T didn't specifically needle T-Mobile this time because they're afraid what unpredictable CEO John Legere might do next in response.