In short, Comcast is moving from a flat cap to usage-based billing.

It is scrapping its 250-gigabytes a month cap and trying a couple different plans in its place. One version will introduce a 300-gig cap and offer additional tiers of service, with bigger caps, along with the ability to buy more chunks of data. Another version also uses a 300-gig cap and the ability to buy incremental blocks of data as needed.

Comcast, which has more than 18 million high-speed data customers, says it will experiment with the two plans in some of its territories.

It also says that in markets where it’s not trying the new plans, it will scrap its data cap entirely until it settles on a new plan.

The move comes as Comcast has taken heat about the way it treats data on some of its proprietary video services, in particular the Xfinity app for Microsoft’s Xbox console.

Netflix CEO Reed Hastings has argued that because Comcast doesn’t count data delivered via that service against its usage caps, it is violating “net neutrality” principles. Comcast says it’s in the clear because that data isn’t delivered via the public Internet but on its own network, and doesn’t plan on changing its policy.

Comcast executives referenced the debate as they introduced the new plans today. “There has been a little bit of noise along with the Xfinity Xbox plan,” said Comcast EVP David Cohen. But Comcast also insists that only a small handful of its users come close to using the 250-gig cap today. The company says median usage runs around 8 gigabytes to 10GB a month.

Other broadband providers, notably Time Warner Cable, have also moved to usage-based pricing. If you take the companies at their word, they’re doing it because they need to charge more money to provide more bandwidth because “our network is not an infinite resource, and it is expensive to build it,” as Cohen says.

But usage-based pricing is also a useful tool to have available if cable TV users really do stop subscribing in large numbers, and replace their pay TV packages with Web video. That gives the cable (and telco) guys a way to replace the video revenue they lose with more broadband dollars. A bonus for them: Broadband subscriptions are much more profitable than video subscriptions.

[Shutterstock/Janos Levente]

Is that good for consumers? There’s an obvious fear that when two big utilities agree to work together, the end result will be higher prices and fewer choices for their customers. So today the two companies are testifying in front of a Senate subcommittee, trying to explain why that’s not the case.

The hearing kicks off at 2 pm ET, and you can watch a Webcast here. But the people who present at these things give out their testimony in advance, and while that reduces any chance for drama, it is helpful for reporters on deadline.

For instance, here’s an interesting argument from David Cohen, Comcast’s executive vice president: If you let us little guys work together, he says, we can take on the really big guys:

“By enhancing the Cable Companies’ and Verizon Wireless’s own products and services, the Joint Venture will compete with similar solutions that AT&T, Dish Network, Google, Apple, Microsoft, and others already have introduced into the marketplace. This, in turn, will spur other companies to respond, perpetuating a cycle of competitive investment and innovation.”

Wait a minute. AT&T and Dish are direct competitors with Verizon and Comcast. And it’s possible that those other guys might be one day, particularly as Google gets ready to start selling broadband and cable in Kansas City. But what exactly is Cohen talking about there?

The footnotes in Cohen’s remarks here are interesting. To back up his argument, he cites the following news items: Google’s Android launch; a Google/Sprint deal that put the search giant’s tools on Sprint handsets; Apple’s iPad launch; the fact that many tech companies have been buying wireless patents; and Google’s pending deal for Motorola Mobility.

In other words: In the future, our competition won’t just be other pipe companies, but other device makers, too. If you take him at his word, things are going to get very interesting.

At a very first glance, some of the new rules imposed by the feds might seem like they require the new company to offer up programming to any online player that wants to pay up.

And technically, they do. But the new rules have plenty of conditions and limits. So the bottom line is you’re not much more likely to get access to “30 Rock” via YouTube, or CNBC via iTunes, then you were before.

The new FCC and DOJ rules do give, say, Google the ability to buy access to some of NBC U shows or channels. But it would require Comcast’s competitors to do the same thing, first.

That is: Unless the people who are reluctant to put their stuff online because they don’t want to upset Comcast go ahead and put their stuff online, Comcast doesn’t have to, either. So it’s theoretically possible, but not probable.

And if it happens, it will happen haltingly. If Viacom sells someone online access to its MTV lineup of reality shows, that might require Comcast to offer up its reality show lineup on Bravo. But it wouldn’t entitle an online outlet to the police procedurals on USA.

The government also gives the option to, say, Netflix, to set up shop as another cable operator, and buy access to all of NBC Universal’s programming. But it would have to buy all of it–just like Time Warner Cable and Cablevision do when they make a carriage deal for NBC U’s shows.

And again, Comcast wouldn’t have to do that unless its peers did. Which means that if Netflix really wanted to set up shop as a direct competitor of the cable guys, it can do so. But it would have to operate exactly like the cable guys, just like the satellite guys did when they entered the market a couple of decades ago.

So if Netflix, or Apple or whoever really wants to offer a full suite of cable programming, at cable prices, it could. But that would be very, very expensive: Analyst Rich Greenfield estimates that the bill for NBC U’s programming alone would run a new entrant $1 billion a year.

Just as, or even more, important, is that those kind of bundled, take-it-or-leave-it deals are exactly the kind of thing that the cord-cutting crowd complains about.

They don’t want to have to pay for USA and Bravo and Syfy and MSNBC–they want to pick and choose channels, or shows. And pay a lot less.

“I don’t think cord-cutting was a major focus” of negotiations, Comcast EVP David Cohen said during a press conference this afternoon. And that may be true!

But the net result reads very much as if Comcast wanted to make sure the government didn’t force it to break its business model. And if that was the case, it got what it wanted.

We filed this appeal in order to protect our legal rights and to challenge the basis on which the Commission found that Comcast violated federal policy in the absence of pre-existing legally enforceable standards or rules. We continue to recognize that the Commission has jurisdiction over Internet service providers and may regulate them in appropriate circumstances and in accordance with appropriate procedures. However, we are compelled to appeal because we strongly believe that, in this particular case, the Commission’s action was legally inappropriate and its findings were not justified by the record.”

As legally inappropriate and unjustifiable as Comcast (CMCSA) might find it, the cable company will abide by the FCC’s order during the appeal. And it will forge ahead with plans to develop more net neutrality-friendly network management techniques by the end of the year. Said Cohen, “We will follow through on our longstanding commitment to transition to protocol-agnostic network congestion management practices by the end of this year. We also remain committed to bringing our customers a superior Internet experience.”

Superior Internet experience until you hit that 250GB broadband cap, that is.