The FCC has always been adamant about the wireless industry being competitive in the US. It's the biggest reason why T-Mobile still exists, actually. The FCC blocked AT&T from buying T-Mobile a few years ago, and Sprint's talks with the FCC and other regulators were netting the same response. In the FCC's annual Mobile Wireless Competition Report, the commission took data from July 1st 2015 through December 31st 2015 to see if there is enough competition among the carriers. What was interesting here is that Verizon claimed the majority of all service revenues in 2015, but they did see a slight decrease over the previous period.
Verizon took about 38.1% of service revenues in the industry in 2015. That's down from 38.7% in 2014. AT&T came in second place, taking 32.4% of the service revenue, which was essentially the same as 2014. Sprint took in 14%, down from 14.9%. Finally T-Mobile gobbled up 13.5% last year, that was up from 11.9% the year before. T-Mobile was the only one that saw their service revenue share increase in 2015, compared to the year prior. Of course, a big part of that is likely due to the number of customers they added in 2015. Officially, T-Mobile added 8.3 million for 2015.
Now on the topic of whether the wireless industry is indeed competitive, the Wireless Telecommunications Bureau basically called it competitive. But did state that the industry is much to complex to be put in such a simple way. Which makes plenty of space, the wireless industry is very complex, not just in plans offered and the networks, but also in the way being competitive would be measured. The Wireless Telecommunications Bureau wrote in their own report that this report "focuses on presenting the best data available on various aspects of competition throughout the mobile wireless ecosystem while also highlighting several key trends."
Of course the CCA (Competitive Carriers Association) and the CTIA both disagreed with the FCC's findings in their report. The CTIA said that the FCC's report shows that "consumers today enjoy unparalleled choice among wireless providers, service plans, and devices, all while wireless industry continues to invest in networks at extraordinary levels." Showing that while the FCC won't come right out and say that the industry is indeed competitive, it is much more competitive than it has been in years past, even with these carriers spending more and more on their network to ensure that they have enough capacity for their ever growing subscribers, as well as staying ahead of their competitors.