Source: T-Mobile

In another turn of events by the scrappy and defiant mobile carrier T-Mobile (NASDAQ:TMUS), the company sent an official letter to the Federal Communications Commission (FCC) this week asking the government entity to block AT&T's (NYSE:T) purchase of some low-band 700 MHz spectrum. The letter comes at time when T-Mobile is looking to expand its low-band spectrum in an upcoming 600 MHz auction next year. 

So, why is T-Mobile making such a big deal over AT&T's pursuit of low-band spectrum when the the self-proclaimed uncarrier is about to offer up bids of its own spectrum next year?

Because it believes AT&T -- and Verizon Communications -- are being greedy with the coveted low-band spectrum already, and T-Mobile says they don't need any more. 

Leaning on a new rule
Last spring the FCC passed a new rule saying that if any one carrier held one-third of spectrum below 1 GHz in any given area then the control of that area would come under review. Essentially T-Mobile's asking the FCC to enforce that new rule right now in parts of Kentucky, Ohio, and West Virginia, where AT&T could have about one-third of the low-band spectrum in certain areas, if its 700 MHz purchase went through. 

Here's what T-Mobile had to say in its official letter to the FCC: 

With this acquisition, AT&T will prove far more able to exclude competitors, raise their costs, damage their businesses and ultimately lessen competition in the Markets. Consumers in the Markets, which have a low population density with a high percentage of low-income consumers, will suffer from reduced competitive choice, less innovation, and higher quality-adjusted prices if the Commission allows AT&T to further entrench its growing duopoly with Verizon.

Harsh words, indeed. T-Mobile also noted that AT&T already dominates some of these areas already, meanwhile T-Mobile has little or no presence in those markets. Of course, there's two sides to every story, and AT&T argues that it's just trying to enhance its network for rural customers. In a blog post AT&T's Vice President of Federal Regulatory, Joan Marsh, took the gloves off and said that it's T-Mobile's fault for not investing in rural areas and said, "I guess un-investment in un-urban markets is the un-carrier thing to do."

What's at stake
T-Mobile is fighting so vigorously against AT&T's low-band expansion because the company needs more of it. Low-band spectrum penetrates through buildings better than high-band spectrum and can cover larger geographical areas using less transmitters. And while T-Mobile's meticulously built out a strong 4G LTE network over the past few years, it still falls behind the competition for overall performance and reliability, according to the latest RootMetrics data

Source: RootMetrics.

The FCC hasn't responded to T-Mobile yet, but as the company has asked the federal regulator to act on its own rules it's likely a response will come soon. If the FCC reviews AT&T's purchase and finds that it does indeed surpass one-third of the 1GHz spectrum in some or all of those markets then it may be forced to change AT&T' s spectrum acquisition.

But all fighting aside, the big picture here for T-Mobile is that it needs to improve its spectrum on its own, and not just fight with AT&T on the sidelines. The carrier has created a viable competitor to the nation's largest carriers and it needs to continue that push to bring better overall performance to more of its customers. Complaining the FCC won't do that -- buying up more low-band spectrum and building out the network in underserved areas will.