For another thing, when Yota switched over from WiMax to LTE, it replaced all its subscriber's USB modems for free. Some missed the giveaway, which led to the spectacle of three-hour queues to pick up their new gear.

Yota was founded in 2007 and used WiMax, then the only 4G technology, to deploy networks in several cities. But when LTE came along with the endorsement of 3GPP, the standards group behind the widely used GSM technologies, most carriers turned their attention to that system. In late 2009 and early 2010, Yota visited every single vendor of WiMax silicon and asked whether they planned to use the faster WiMax 2 standard, Khachaturov said. Each said it would do so only if Yota committed to a large order. So Yota jumped on the LTE bandwagon.

The advantage would be a much larger ecosystem of suppliers for both network equipment and smartphones and other customer devices. But first, Yota had to persuade the Russian government to allow the use of LTE in the country. Then it helped the government create standards for using it. In the end, the government gave Yota seven months to switch over from WiMax to LTE. All its WiMax cities need to be converted by Sept. 1.

When it embraced the new technology, Yota also decided to get on board with the internationally standard way of using the frequencies it had licensed in the 2.6GHz band. That meant a change from having its uplink and downlink in one band to using two paired spectrum bands. This lets Yota take advantage of FDD (frequency-division duplexing) technology, which gets the most support from network vendors and device makers, Khachaturov said.

The problem was, Yota had to use its existing WiMax band for one half of its LTE network. It proved impossible to run the networks simultaneously and do the transition gradually, because of interference between LTE and WiMax signals. Yota was able to run tests on a small LTE network in one city, but there was no way to turn on a large, citywide LTE system without first shutting down the current WiMax network.