AT&T is bringing back unlimited data. The number-two wireless carrier discontinued its original unlimited plans years ago, but it's resuscitating the all-you-can-eat option as a cross-promotion with its DirecTV and U-verse television services.

Unlimited data will cost $100 per month for a single smartphone, and you'll be able to add additional smartphones for $40 per month each. If you bundle four smartphones on a single plan, you'll get a credit that makes the fourth line free. That means you'll be paying a total of $180 per month (excluding taxes and fees) for unlimited data, talk, and text on four lines. Frustratingly, you'll have to pay the full $220 for the first two months before the credit kicks in. This plan also prevents you from using the tethering or mobile hotspot feature of your smartphone. That's a major limitation, especially since this plan is designed for heavy users.

Cord-cutters need not apply

Before you get too excited about the new plans, note that you'll have to be a DirecTV or U-verse subscriber to sign up for unlimited data. If you're a cord cutter, don't live in a U-verse market, or can't install a DirecTV satellite dish, you'll have to settle for a standard Mobile Share plan. However, if you do sync up your television service with your AT&T plan, you'll also get another $10 off your bill monthly, per the company's existing promotions.

It's clear where the company is going here: it's leveraging its new DirecTV acquisition and existing U-verse TV services to promote video streaming on the go. While the plan itself doesn't bundle in specific home TV packages, it's designed to work hand-in-hand with DirecTV and U-verse's out-of-home streaming apps. It just so happens that watching lots of video quickly burns up your data allowance — and AT&T's more than happy to offer an unlimited plan to fix that problem. Of course, if you'd rather just watch Netflix and use your AT&T phone separately, you'll have to keep an eye on your data usage. Such is the power of mergers.

Assuming you're a DirecTV or U-verse subscriber, you'll need to take a close look at your usage to see if this unlimited plan makes sense for you. If you have four smartphones, the pricing just about lines up with the 20GB Mobile Share Value data bucket, which costs $200 per month.

$40-per-month tablet access fee is steep

That's not too bad, but the pricing gets trickier when you factor in other internet-connected devices. Adding a tablet to the unlimited plan costs a steep $40 per month extra, compared to just $10 on a Mobile Share Value plan. AT&T notes that you can add a tablet for just $10, but it'll only have 1GB of data to work with if you do, compared to full access to the entire data pool on a traditional shared plan. And if you still have someone using a basic cellphone on your plan, it's probably best to avoid unlimited: adding a feature phone to the account costs $25 extra per month, compared to just $15 on the standard plans. Considering feature phones essentially don't use data, the price hike is hard to swallow.

In addition, keep in mind that if you only have one or two heavy users on your account, there's really no need to pay the extra to give unlimited data to every line. However, if you're still holding onto a grandfathered unlimited plan — which requires separate charges for minutes and texts — it might make a lot of sense to upgrade to the modern unlimited plan. Unfortunately, it doesn't appear there's a way to upgrade a single line on a Mobile Share Value plan to unlimited.

"Unlimited" means unfettered access up to 22GB per line

It's fair to ask just how "unlimited" these unlimited plans are — in the past, AT&T essentially treated its grandfathered unlimited plans as soft-capped 5GB plans. After a complaint from the FCC, AT&T now gives unlimited plans unfettered access to 22GB per line. Over that limit, you'll be subject to slowdowns if network congestion demands it.

As for the competition, most other wireless carriers no longer offer true unlimited data plans, though T-Mobile's similar unlimited plan costs $95 per month for a single smartphone. Unlike this AT&T plan, it does provide a data allowance for tethering. T-Mobile also offers a separate feature designed to promote mobile video streaming, called Binge On, which doesn't count certain, standard-definition video streams against your data cap. While it's far more limited, T-Mobile's approach doesn't cost any more money to use on an existing plan. However, the service has also drawn the ire of net neutrality advocates.

The new AT&T plans will be available starting tomorrow, and if this one doesn't strike your fancy, AT&T promises that this is just "the first of many integrated video and mobility offers" planned for 2016. Make no mistake: AT&T wants to be your one-stop shop for wireless service and home TV.

Update March 22nd, 2016: Added note that this unlimited plan completely blocks tethering from your phone.