T-Mobile announced its latest challenge to the wireless competition on Tuesday with a new Uncarrier 8.0 "data stash" feature for some of its non-contract smartphone plans. It's like rollover minutes for 4G data, with a couple caveats, but also a way to get 10GB of promo data for free.

John Legere, CEO of T-Mobile, told Yahoo Tech's David Pogue in an exclusive interview about the company's newest "data stashing" plan for its contract free customers on Tuesday.

An Early Gift to Subscribers

It's like an early holiday gift for T-Mobile subscribers, though for Legere, it's even better than the 'most wonderful time of the year'.

"Uncarrier move time is my favorite time of all," said the usually ebullient Legere, this time managing to sit down for an interview with Pogue.

That doesn't mean Legere forgot to bring the heat, as well. "The tagline is, 'It's your data. What you don't use, you won't lose,'" said Legere.

"Think of it as data rollover," he continued, promptly comparing the current state of wireless data to a game that's rigged from the start so the house wins every time.

"This is a philosophical, principle-based attack on changing a stupid, broken, arrogant industry," said Legere.

Why is he so hyped up against the status quo of wireless data?

Well, according to Legere and T-Mobile's research, a huge number of normal post-paid contract customers -- those who generally buy 2-year contracts with a set limit for data -- are paying for data they don't use. On top of that, they then have to pay penalties for the odd month when they go over their limit.

Added up, Legere claimed contract wireless customers waste a total of $50 billion every year on data they never use.

The Details on the Data Stash 

Uncarrier 8.0's "data stash," according to Legere, is going to change that.

With the data rollover feature, some customers on T-Mobile non-contract wireless plans will immediately begin seeing the benefits without signing up for any new coverage, buying any new phones or tablets, or doing anything else.

They just get to start rolling over their unused 4G LTE data for a rainy day -- automatically.

And it's not a promotion. Like all Uncarrier moves, it's a new, permanent part of T-Mobile's prepaid coverage plan structure. "I think this is really going to shake up the industry," Legere said.

Promos and Caveats

There is, however, both a promotional aspect to Uncarrier 8.0's "data stash" plan, along with some inevitable restrictions that apply.

First, the promo:

According to T-Mobile's announcement, while the data stash feature is automatically open to existing user on specific coverage plans, new customers will be given 10GB of data for free to start their "stash" off with.

From then on, any unused 4G data, rounded up to the next megabyte, will automatically be banked into the stash as well. And there's no limit to how many gigs you can have in your trove of unused data.

Now, the caveats:

First of all, don't think you'll be banking terabytes of data into your stash if you keep with the same plan for years. While data rolls over from month to month, the 4G data you're stashing isn't immortal. It has a 12-month lifespan.

Fair enough, but there are a few more important restrictions regarding who gets to stash their data and who doesn't.

"Data stash" is not available for pre-paid customers at all, and users with the post-paid Simple Choice Plan have to have at least the extra 3GB 4G data for smartphone option (or above) or at least the 1GB option for tablets. However, this applies to individuals, family, or business plans in that category.

What do you think of Uncarrier 8.0? Are you thinking of changing wireless providers, now that they've offered an equivalent to the old Cingular rollover minutes feature, but for the modern data-driven age?

Let us know in the comments below!