The latest measure of America’s mobile networks shows consumers are enjoying faster speeds on their smartphones and tablets, as network improvements have outpaced increasing usage so far. But there were some troubling signs in the data collected by testing firm Ookla, which makes the popular Speedtest app.
In a new report covering the first half of 2017, Ookla said the average download speed on U.S. mobile networks reached 22.7 megabits per second, 19% faster than the same period in 2016. That’s fast enough to download all 14 songs in Kesha’s new album Rainbow in about 38 seconds. Upload speeds lagged behind however, averaging just 8.5 Mbps, a 4% improvement from last year.
But don’t get too impressed. Mobile network speeds in the United States lag far, far behind much of the rest of the world. For the first half, the U.S. ranked 65th in upload speed, Ookla said, just behind Mongolia. For downloading, the U.S. was 44th behind Fiji and Germany. And speeds declined on average from the first quarter of the year to the second quarter, possibly indicating the impact of unlimited data plans that are prompting consumers to download more music and video on their phones than ever.
T-Mobile (TMUS) had the fastest average score nationwide of 23.2 Mbps, followed by Verizon in second place 21.2 Mbps, Ookla said. AT&T took third at 20.1 Mbps, and Sprint trailed at 15.4 Mbps.
Get Data Sheet, Fortune’s technology newsletter.
But Ookla said its users were seeing an impact from the spread of unlimited plans at AT&T and Verizon (VZ) in the second quarter.
“Verizon has been able to maintain solid performance in areas of high traffic, though a drop in performance has been seen since Verizon launched unlimited,” Ookla said in its report. AT&T (T) has kept up performance “for the most part,” but showed a “notable drop” after expanding its offerings with a cheaper unlimited plan that capped speeds at just 3 Mbps.
Most of the performance drops came from a big jump in customers experiencing the very slowest of speeds, under 5 Mbps, Ookla said. That may mean that AT&T and Verizon are not suffering from complete network overload due to unlimited plans, according to the firm. “Others have argued that these networks may be saturated,” Ookla noted. “However, if they were, we’d expect to see the number of tests at every level of speed decrease. Our data does not bear this out and it seems likely we’re seeing reduced performance due to high usage de-prioritization and consumer plan choice.”
Even though Sprint (S) came in fourth, Ookla said it showed a big improvement as it sped up 24% from last year. With considerable unused airwaves in the 2.5 GHz band, Sprint “still has a lot of room for improvement and a lot of opportunities for tapping into its treasure trove of 2.5 GHz spectrum,” Ookla said.
Ookla said it calculated the average speeds by combining the results of 14 million Speedtest app results from 3 million users. That’s similar to how OpenSignal calculated its speed rankings last month, but quite different from Rootmetrics, a testing firm that employs professional testers who drive around the country and measure network performance.
Speedtest in its report also crowned T-Mobile as the fastest network and also said unlimited plans were slowing speeds, while Rootmetrics said Verizon was fastest and unlimited plans were not hurting performance.
The carriers frequently cite the test results in TV ads and marketing materials. On Wednesday, T-Mobile CEO John Legere spent almost as much time bashing his rivals’s slowing speeds as he did touting his company’s new partnership with Netflix. “Their networks choke and slowdown,” Legere said about three minutes into his opening remarks. “T-Mobile, our unlimited, it’s America’s best.”
