AT&T just introduced two new 'unlimited' data plans - here's everything you need to know

AT&T is introducing two new "unlimited" data plans to better compete with recent similar offerings from Verizon, T-Mobile, and Sprint.

The carrier has had an unlimited plan for some time, but previously it was only available to subscribers of its DirecTV or U-Verse TV services. Earlier this month, it lifted that requirement.

Now, it's reworking the costs and features of its offer altogether. The new plans will become available on March 2. AT&T says current subscribers will be able to switch to the new plans.

Here's the rundown:

• The first new plan, AT&T Unlimited Plus, starts at $90 a month for a single line. Two lines cost $145 a month, each additional line costs another $20 a month after that (for up to eight lines). That's down from $100 a month for a single line, plus $40 a month for every additional line, under the previous plan.
• If you subscribe to the Unlimited Plus plan, AT&T will take $25 off the price of a subscription to its DirecTV, U-Verse TV, or DirecTV Now service each month. (AT&T still does not count all of those services against your data cap, a controversial practice known as zero-rating.) AT&T says this is a limited-time promotion, and that it'll start applying the $25 credit after "2-3 billing periods." 

• You can add a tablet to the plan for another $20 a month, and a wearable for another $10 a month.
• The Unlimited Plus plan will now include 10GB of LTE mobile-hotspot data, which lets you use your phone as a WiFi hotspot. Once you hit that limit, mobile-hotspot speeds will be throttled down to 128Kbps, which is close to 2G speeds. Previously, AT&T did not include mobile-hotspot data at all with its unlimited plan.
• The Unlimited Plus plan includes "high-definition" video streaming, but you'll have to turn off AT&T's Stream Saver feature - which caps video streams at a less-sharp 480p resolution by default - to use it.
• Like before, AT&T says it might slow your connection speeds in areas of network congestion if you use more than 22 GB of data in a single pay period.

Besides Unlimited Plus, AT&T is offering a second, more affordable "unlimited" plan called AT&T Unlimited Choice. That starts at $60 a month for a single line, $115 a month for two lines, and another $20 a month for each additional line after that.

However, it caps all video streaming at "about 480p," and caps all speeds entirely at 3Mbps, which isn't terribly fast by modern standards. Once again, AT&T says it might slow speeds in areas of congestion if you use more than 22 GB of data in a given month.

In either case, the rates above do not take into account monthly fees and taxes, so they'll be a little more expensive than advertised. (A caveat that applies to every carrier but T-Mobile.) You'll also have to enroll in auto-pay billing - otherwise, AT&T says a single-line plan will cost another $5 a month, while a multi-line plan will cost another $10 a month.

While carriers continue to stretch the meaning of "unlimited" - a word that means "not limited or restricted in terms of number, quantity, or extent" - the recent re-interest in the concept has set off a fluid competition, as Verizon and AT&T attempt to slow market share gains from the fast-growing T-Mobile, which kickstarted the revival this past summer, and fourth-place Sprint.

In this case, the lowered entry price and mobile-hotspot data should make AT&T's unlimited offering a bit more competitive with its peers. It is still the most expensive of the bunch, however.