US operators Verizon and AT&T experienced falling network speeds following the launch of their unlimited plans, allowing T-Mobile US to gain further ground on its rivals, a new OpenSignal report revealed.

The findings somewhat backed up claims by T-Mobile US CEO John Legere (pictured), who accused both AT&T and Verizon of “choking” with their unlimited offerings, stating both companies had seen significant network slowdowns since launching the tariffs, while T-Mobile’s network had become faster.

According to the wireless signal mapping company, both Verizon and AT&T experienced “a marked decline” in 4G speeds in new tests, almost six months after reintroducing unlimited plans.

The impact of unlimited hit Verizon the most, with tests showing the operator’s average download rates fell 2Mb/s to 14.9Mb/s in the space of six months between the release of OpenSignal’s last report on the state of mobile networks in the US.

AT&T had an average 4G download speed of 12.9Mb/s this time round, down from 13.9Mb/s in the February report.

Rising speeds
Meanwhile, T-Mobile US and number four player Sprint did not experience “any adverse effect on their speeds”, according to OpenSignal’s tests.

Conversely, both operators actually saw LTE speeds climb upwards in the last six months, with T-Mobile US surpassing Verizon with average LTE speeds of 17.5Mb/s, up from 16.7Mb/s.

Sprint also saw an increase in LTE download speeds from 9Mb/s to 9.8Mb/s between reports, although this wasn’t enough to lift the operator out of last place.

OpenSignal said the drop in speeds for AT&T and Verizon was likely caused by “congestion”, explaining increased demand through more customers or more data usage was causing average connection speeds for all users to drop.

“We may well see this trend continue as more AT&T and Verizon customers take advantage of these new unlimited plans,” the company stated in its report.

OpenSignal noted T-Mobile US and Sprint did not experience the same network issues because the companies had been offering unlimited services to consumers for years.

4G access
T-Mobile US also surpassed Verizon on LTE availability, “but it was a very close call”. Testers found they were able to find a 4G signal on T-Mobile 90.9 per cent of the time, compared to 89.8 per cent of the time on Verizon.

Indeed, OpenSignal found in its previous report the company was closing the gap on Verizon for 4G availability.

“T-Mobile’s first place finish may come as a surprise considering Verizon’s long deserved reputation for providing the best mobile coverage in the US,” OpenSignal stated.

However, OpenSignal noted its 4G availability metric doesn’t measure geographic coverage, but rather provides an insight into how often subscribers are able to access a 4G service, regardless of location.