T-Mobile has won a landmark court victory over U.S. carriers AT&T and Verizon Communications, after the FCC agreed to work with the fourth largest carrier to change data roaming charges.

The case said both U.S. carriers charge smaller competitors too much on their own network in roaming charges. AT&T and Verizon both offer the roaming service to smaller networks, which may not have established spectrum in a few states.

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The Federal Communications Commission (FCC) will look over proposed rates by both U.S. carriers and make sure they do not overstep the mark. The FCC is now able to readily intervene, if either of the carriers push the boundaries.

T-Mobile claims AT&T charges 150 percent over the average on data roaming, and Verizon has also been noted for its aggressive structure when it comes to data roaming.

The high rate may cause stagnation in the wireless industry if no small service is able to afford large data roaming charges. AT&T and Verizon have also been known for not negotiating on prices, making it even harder for startups to prevail.

T-Mobile still has a lot of ground in the U.S. to cover, and is prepared to invest billions in spectrum sales over the next two years. The fourth largest U.S. carrier announced 2.6 million new subscribers in the third quarter, beating the three other carriers.

The victory in court comes days after T-Mobile's CEO John Legere announced another incentive to move to T-Mobile: Data Stash. The new feature will allow users to stash unused 4G LTE data and move it over to next month, staying in the stash for 12 months.

Data Stash will be available to all T-Mobile Simple customer plans over 3GB. It is the first program to include 4G LTE data, previously MVNO and Verizon offered the program for 3G.

TagsT-Mobile, AT&T, Verizon wireless, U.S. carriers, data roaming, FCC