The battle lines are shifting in the U.S. mobile market. For more than a decade Verizon and AT&T have been the dominant operators in the U.S., but in the last few years, T-Mobile has reemerged as a viable competitor to the country's two mega-carriers. Using spectrum gained in the aftermath of AT&T's failed attempt to take over the then 4th-place operator, T-Mobile launched its first LTE service in 2013, three years after the mobile broadband technology’s debut in the U.S. In those three years, T-Mobile has undergone a remarkable transformation. It passed Sprint in total subscribers last year, and our data indicates T-Mobile is now challenging the nation's two mobile behemoths in network performance.

By OpenSignal's measurements, nowhere has that resurgence been more pronounced than in our most recent test period. T-Mobile won top awards for four out of the six network metrics we tested for — including all three speed categories — in a 71-day interval this spring and summer. While T-Mobile for some time has been contesting the top spot for speed, the big surprise was the rapid improvement in T-Mobile’s LTE availability that we saw in our data. Our users found Verizon is still the leader when it comes to providing a consistent LTE signal, but T-Mobile surpassed AT&T in 4G availability in our latest tests and is now closing the gap with Verizon. (Though AT&T and T-Mobile sometimes refer to HSPA as 4G, OpenSignal defines 4G as LTE only. We use the two terms interchangeably throughout this report.)

In our newest State of Mobile Networks report for the U.S., OpenSignal compared 2.8 billion tests conducted by OpenSignal users across the four major U.S. operators. Starting in May, OpenSignal made some adjustments to both the way we collect data from our smartphone apps and the methodology we use to parse that data. The update allows us to make more measurements, examine new types of network metrics and hone the precision of the measurements we've always collected, helping us isolate the typical consumer mobile experience more effectively (for more details, see our recent blog post). The changes haven't affected our overall rankings of networks around the world, but for sake of analytical rigor we aren't making any direct comparisons between results collected from the two different methodologies.

For this report we also took a much deeper dive into regional results than we have in the past. We examined 4G speed and availability in 31 major U.S. metro areas to see how how the operators compared on a city-by-city basis. First, let's take a look at how U.S. operators fared in speed.

A tight race for the speed crown

T-Mobile won OpenSignal's 4G speed award in our latest results, but just barely. It averaged downloads of 16.3 Mbps in OpenSignal’s tests, but second-place Verizon was close behind with an average speed of 15.9 Mbps. The two operators have been locked in a 4G speed battle for the last several years. For instance, in our last U.S. report we recorded a draw for Verizon and T-Mobile in 4G speeds. In the current test period, the statistical margins separating the two results were razor thin, but our measurements found T-Mobile scored the win.

We saw that competitiveness reflected in our regional results as well. In our breakdown of 31 large metro markets, T-Mobile won our award for fastest 4G speed outright in 6 cities, including New York City (20.4 Mbps), while Verizon won the LTE speed metric in 7 cities, including Los Angeles (20.0 Mbps) and San Francisco (21.6 Mbps). In 11 other markets, Verizon and T-Mobile both contested the award for fastest speeds, but the results were close enough to produce statistical ties. And in all but one of the remaining 7 metro areas, either T-Mobile or Verizon (often both) had a share of our speed award due to three-way draws with AT&T and Sprint.

Though AT&T didn't factor in the close-fought battle for top speed nationally, we still recorded a respectable 12.8 Mbps average speed for Ma Bell nationally. It also put on some good performances regionally, winning our fastest LTE speed metric in one city (Austin) and tying for first in six more. Meanwhile, Sprint is still struggling to catch up with its competitors in LTE performance. OpenSignal tests on Sprint’s network found average 4G download speeds of 9.4 Mbps. Sprint has been making upgrades to its networks intended to boost its bandwidth, but so far those improvements don't appear to be having a big impact on the network speeds our users measure. Sprint, however, did make a showing in two of the cities we examined, tying for our 4G speed award in Cincinnati and Denver.

3G data services are increasingly becoming a non-factor in the U.S. as LTE coverage spreads and consumers increasingly upgrade to 4G-capable devices, but on the occasions customers are forced to contend with a 3G connection, T-Mobile and AT&T subscribers were at a distinct advantage. Our users measured speed three to five times faster on those operators’ HSPA connections than on Verizon and Sprint’s CDMA EV-DO connections. T-Mobile won our 3G speed award, averaging downloads of 4.6 Mbps in our tests, while AT&T came in second with an average download speed of 3.0 Mbps.

As T-Mobile had both the fastest and 4G and 3G connections in our tests, it won our overall speed award with an aggregated download metric of 14.0 Mbps. Though Verizon had the slowest 3G connections in the country, it didn't have much bearing on its overall speed tests. Verizon was hot on T-Mobile's heels with an overall speed of 13.5 Mbps. Because of its superior 4G signal availability Verizon customers rarely had to resort to its sluggish CDMA network.

The long arm of T-Mobile

Once again, Verizon cemented its place at the top of our rankings when it came to providing a consistent LTE signal. But it's facing an increasingly aggressive challenger in network availability, and it's not Verizon’s traditional arch-rival AT&T; instead it's T-Mobile.

Rather than measure geographical coverage, OpenSignal's availability metric tracks the percentage of time customers can access a particular network, whether they're indoors or out, in the city or the countryside, moving or stationary. On Verizon's network, OpenSignal users were able to latch onto an LTE signal 86% of the time. T-Mobile, however, was less than 3 percentage points behind Verizon. Our users were able to get an LTE connection 83% of the time on T-Mobile’s 4G network. In our test period, T-Mobile leapfrogged over AT&T, for which we measured LTE availability at 80%.

T-Mobile's recent gains shouldn't come entirely as a shock. For the last year, T-Mobile has been dispensing with the notion that it’s merely an urban-focused operator by building new 4G networks in rural areas. It's also made use of recently acquired 700 MHz airwaves to give those networks more reach. 700 MHz's low frequencies mean signals propagate further in rural areas and penetrate deeper into buildings in urban areas — two factors that help explain its rising availability ranking.

Still, T-Mobile has some work ahead of it if it wants to match Verizon signal for signal. In our regional analysis, we found Verizon clearly dominated the availability charts. Verizon won our best availability award outright in 17 of the 31 metro areas we examined, and in the remaining 14 markets, Verizon shared 1st prize with either T-Mobile or AT&T due to statistical ties. Our data may show that T-Mobile is in the race for best 4G availability, but Verizon is still clearly the operator to beat.

As with 4G speed, Sprint was a distant fourth in 4G availability in our measurements. OpenSignal users could access the Sprint LTE network only 70% of the time. But there was one area where Sprint did shine brightly: network responsiveness. Our latency metric measures the reaction time a customer experiences when accessing mobile internet services. A low-latency connection means web pages begin rendering more quickly and customers experience less lag time in real-time communications apps like VoIP and video chat. Sprint led all operators with the lowest (best) 4G latency of 57 milliseconds in our tests. our users found that T-Mobile had the most responsive 3G network, measuring its latency at 99ms.

Looking for a 4G edge

If there is one thing clear from this report, it's that T-Mobile is challenging the established powers in the U.S. mobile market, putting its resources to bear in building both high-performance and highly accessible mobile broadband networks. Whether T-Mobile can keep up the pressure remains to be seen. Verizon and the Un-carrier are neck and neck in LTE speed, and while T-Mobile continues to improve its 4G availability, the other operators aren't exactly standing still. There's a massive spectrum refarming campaign going on the U.S., as every operator looks to scavenge old 2G and 3G airwaves to breath new capacity and reach into their 4G networks.

One of the biggest new developments in the U.S. mobile market is taking place as this report goes to publication. The Federal Communications Commission is auctioning off as much as 126 MHz of TV spectrum to mobile operators. Those 600 MHz airwaves will be the lowest-frequency airwaves to which operators will have ever had access, allowing them to build far-spanning networks. In addition, the new capacity that spectrum will bring will let operators boost speeds and design powerful new LTE-Advanced systems like the ones we're seeing deployed across Europe and Asia. But the FCC has set a minimum price for those airwaves of $88.6 billion, so who gets that spectrum — and who gains the advantage in the next round of 4G wars — may largely depend on who's willing to write the biggest check.