John Legere, T-Mobile US CEO, called for RootMetrics to be “banned as an independent source for network benchmarking”, after it named rival Verizon as the best network performer in the US during the second half of 2015.

In its twice per year study, RootMetrics said Verizon had the best network for the fifth consecutive period, based on its study of network performance in six categories; overall, reliability, speed, data, call and text performance.

In contrast, T-Mobile US finished bottom, based on an overall performance score.

RootMetrics’ conclusion however differs from a similar study conducted by rival testing firm OpenSignal, which found that T-Mobile had closed the gap with its big-two rivals, including beating them in some areas.

Legere, who has taken issue with RootMetrics in the past, said in an emailed statement that the company “manipulated their testing of the T-Mobile network” by turning off its Voice over LTE (VoLTE) feature when conducting the study, “a technology that is on every single phone we sell”.

The outspoken CEO claimed VoLTE handles roughly 50 per cent of calls made on its network, equating to 250 million calls a day.

RootMetrics found Verizon’s network was first in five categories, and tied in second in text performance, with nearly every metric placing AT&T as number two.

The company also reportedly said it will begin to test VoLTE from the first half of 2016.