Score another win for the “Un-carrier.” Ars Technica notes that T-Mobile has now “won a declaratory ruling that could force AT&T and Verizon Wireless to charge lower prices for data roaming.” Essentially, T-Mobile has been arguing that America’s two biggest carriers have been charging unfairly high prices for data roaming that artificially kept the price of its services higher than it should be.

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A decision made by the Federal Communications Commission’s Wireless Telecommunications Bureau may mean that T-Mobile and other small carriers will have a better chance of successfully challenging the rates they pay because the bureau largely agreed with T-Mobile’s proposed guidance for what constitutes commercially reasonable roaming charges.

Verizon, of course, is none too happy with the ruling and the carrier tells Ars that “it is deeply troubling that the Wireless Bureau has changed a fundamental wireless rule in ways that discourage investment and unfairly advantage one company over others, and has done so without a Commission vote, as required by law.”

Sprint, for what it’s worth, said that it supported T-Mobile’s petition, which makes sense since it would presumably like to pay less on roaming fees as well.

Whether this ends up meaning lower wireless bills for consumers is anyone’s guess, though, as it’s entirely possible that the smaller carriers will use their potential roaming savings to bolster their networks, which are still in real need of improvements.