John Legere, CEO and president of T-Mobile USA, makes an announcement during an event about new contract pricing last year in New York City. (Photo by John Moore/Getty Images)

Get ready to hear a lot about the future of Music Freedom.

T-Mobile's free music streaming service could soon find itself in the middle of a high-stakes battle over whether Internet service providers should be able to give Web companies preferential treatment on their networks. Music Freedom is a so-called zero-rated app that offers data-free access to services like Rhapsody, Pandora and iTunes radio. (With zero-rated apps, either the network operator or the content provider picks up the cost of the data that users consume.)

Zero-rated apps are particularly popular in parts of the world where it is very expensive to download data to watch a movie or browse the Web. For example, Facebook Zero and Wikipedia Zero, are both available in scores of countries around the globe. Content companies in the United States, from to eBay, are also experimenting with subsidized data. In Slate's case, according to the Wall Street Journal, waiving data fees increased podcast downloads more than 60 percent.

But whether or not those apps would be allowed in the United States under a far-reaching net neutrality plan proposed by President Obama earlier this week isn't yet clear. Obama called on the Federal Communications Commission to adopt strict rules that would forbid Internet service providers from charging content companies (like Netflix) to get priority access to consumers. Most of the debate around the rules has centered on broadband service to homes, but Obama advocated for applying them to mobile Internet providers, as well.

That means zero-rated apps in which the content company covers users data costs could violate a strict interpretation of the principle of net neutrality, some industry observers say.

Earlier this week, the Verge pressed John Legere, the fiery chief executive of T-Mobile, on whether he could reconcile Obama's approach to net neutrality and his Music Freedom app. Legere issued a string of tweets in response. But he didn't exactly address the zero-rating issue, other than to say this:

But the mobile phone industry, which wants to avoid being part of any new FCC net neutrality rules, is taking up the cause of Music Freedom. On Wednesday a top telecom lobbyist described zero-rated apps to me as "consumer-welfare-enhancing" add-ons that do no harm to anyone. (Strict neutrality advocates would point out that those sort of services might disadvantage a small streaming music start-up that doesn't have the wherewithal to partner with a big provider like T-Mobile.)

Expect mobile phone companies to keep hammering on the issue as the net neutrality debate rolls along, leveraging the tension between something consumers -- especially those on lower-cost, restricted plans -- really seem to enjoy and strong open Internet protections. That means how you reconcile an Obama-style set of rules for the open Internet with the public's hunger for subsidized apps is one more thing for the FCC must wrestle with as it goes about crafting net neutrality rules.

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