T-Mobile today revealed a new, $70 unlimited plan called "T-Mobile One," which aims to shake up and simplify the carrier's plan structure. As with all of these things, it's pockmarked with caveats and asterisks, but it's still a pretty good deal. I spoke to T-Mobile CTO Neville Ray and CMO Andrew Sherrard today to get things clear.

What's the basic deal?

T-Mobile thinks that people don't want to have to count data, and would prefer unlimited plans. So it's putting a lot of marketing behind a new unlimited plan that costs $70 for one line, $120 for two lines, or $140 for three lines. Additional lines beyond that cost $20.

So unlimited is new here?

Nah, T-Mobile has had unlimited for years. I'm on a T-Mobile unlimited plan myself. Primarily, what it's doing is knocking $25 off the previous unlimited plan to reflect the savings created by the Binge On video-quality-reduction system.

"We've learned a lot from Binge On ... and we found a way to deliver a great video experience, drive network savings, and now pass that value back to the customer," Ray said.

Is T-Mobile getting rid of all of its other plans?

No. This was the most confusing part of this morning's announcement. T-Mobile's $50 2GB plan and $65 6GB plan will still exist, Sherrard said, although he reserved the right to yank them "over time" and "eventually." The only real immediate change is that the $70 T-Mobile One plan is replacing the previous $95 unlimited plan.

"We'll still have the rest of the Simple Choice lineup, you can still go buy that $50 plan," Sherrard said.

The Simple Choice plans will still be better deals for people who don't use a lot of data, especially because they have rollover data that accumulates from month to month. They'll also be better deals for people who tether their phone to a PC.

Is it truly unlimited, for all uses and services?

Not without some add-ons. For instance, all video will be degraded to 480p resolution, as it currently is with T-Mobile's Binge On feature. Full-quality video will now be a $25 option, bringing the $70 plan back up to the previous $95. You don't get LTE tethering; 5GB of that costs $15. Also, if you use more than 26GB per month and you're in a place with a congested network, other users on the same cell tower will be served first.

Some people feel very strongly about tethering, but Ray said only a "small volume" of customers use it at all. And only 0.8 percent of T-Mobile subscribers turned off Binge On to watch full-resolution HD video, Sherrard said. So it's ditching things most people don't use (although the few who do are super passionate.)

Do T-Mobile subscribers have to switch to T-Mobile One?

Also no. You can keep your existing plan. Sherrard agreed, for instance, that if you have the two-line $100 unlimited deal that was out for a while, it's a better deal than the new plan.

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"Anybody who has any existing rate plans, they can keep them forever," Sherrard said. In those words. "Nobody has to change, we're not going to migrate anybody over."

Is this the cheapest unlimited plan on the T-Mobile network?

For more than two lines, yes. For one or two lines, the MetroPCS $60/55 unlimited plan is cheaper.

What are competitors doing about this?

Sprint immediately announced an extremely similar plan that comes out at $20 cheaper for two lines. T-Mobile sneers at Sprint's network quality, and it's true that while Sprint has made big strides over the past year (as shown in our Fastest Mobile Networks results), T-Mobile is still ahead of Sprint on LTE speed and coverage nationwide.

"Sprint was a discount carrier before this morning, and they just reinforced that again," Ray said.

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