T-Mobile is fixing the two biggest flaws in its unlimited plan, one day after Verizon launched its own

One day after Verizon launched its own unlimited data plan, T-Mobile is making changes to its unlimited counterpart to keep up.

The carrier announced on Monday that, starting on February 17, its T-Mobile One unlimited plan will stream video at "HD" quality by default. Currently, the One plan caps all video over mobile data at a less-than-HD resolution of 480p unless subscribers pay $15 for a "One Plus" add-on, or $3 for a 24-hour "HD day pass."

Beyond that, the One plan will also include up to 10GB of LTE mobile hotspot data, which allows you to use your phone as a mobile WiFi router. Once that 10GB point is hit, T-Mobile will send that back to 3G speeds. Today, the carrier throttles all hotspot data to slow 2G speeds, and requires customers to pay for a $25 "One Plus International" add-on to push that to unlimited LTE speeds.

The moves address what are arguably the two biggest complaints customers have had with the One plan to date, and bring T-Mobile's offering to near-parity with the major features of Verizon's unlimited plan. Verizon promotes the same HD video streaming and 10GB of LTE hotspot data in its plan today.

T-Mobile says subscribers will have to activate the features manually in the T-Mobile app or website, but did not say whether that will be required daily, or whether they will be turned on by default every day after they are activated. It also did not say if that HD video will be capped at a 720p resolution, the minimum threshold for high-definition video, or if it will allow for higher-resolution streams.

The move also allows T-Mobile to more clearly undercut Verizon on price. Its One plan will still start at $70 per month for a single line, while Verizon's "introductory" unlimited plan goes for $10 more. The carrier says it will run a promotion that gives two lines of T-Mobile One for $100 total, too, instead of the usual $120. By comparison, Verizon's unlimited plan offers two lines for $140 per month.

T-Mobile is quick to note that its rates include all taxes and fees, though, which drive up Verizon's costs by a few dollars more. Verizon does offer alternative, data-capped plans for cheaper, however, whereas the One plan is the only offering T-Mobile advertises on its site.

T-Mobile's changes further what has become an increasingly heated competition among mobile carriers over newly revived unlimited plans. T-Mobile's One plan kicked off the trend in earnest, but all four of the major carriers now provide an unlimited offering in some form - though AT&T's is only available to subscribers of its DirecTV and U-Verse services.

Verizon joined the fray on Sunday, at a time when the growth of its mobile division has largely slowed, while T-Mobile has steadily gained ground on Verizon and second-place AT&T. According to a recent study by mobile analyst firm OpenSignal, T-Mobile has also caught up when it comes to fastest network speeds. Verizon still covers a wider swath of the country, however.

All that said, the updated One plan still features the same caveat as every other so-called "unlimited" plan: It's not technically unlimited. T-Mobile says subscribers who use more than 28GB of data in a given month may see their speeds reduced due to "prioritization" in congested areas. For Verizon, that limit is 22GB. Sprint and AT&T give similar warnings with their unlimited plans, too. 

We'll keep an eye out for any other caveats when the new One plan goes live on February 17.