"What we had to do was somehow deploy and LTE network without switching it on at all, and then overnight, we had to switch off WiMax and switch on an LTE network that had never been switched on before," Khachaturov said.

Yota had WiMax networks in five cities, but it went straight to Moscow, where it had about 300,000 subscribers. The company rolled out 1,400 LTE base stations at its existing WiMax sites in a project that took two and a half months. It did some radio planning, but no testing or network optimization until the commercial launch. On May 10, Yota launched LTE in Moscow and one other city, Krasnodar.

"It actually somehow worked," Khachaturov said. Yota later did the same thing in the city of Sochi, and it has two more to go.

However, the overnight swaps from WiMax to LTE delivered far less than the doubling of speed that Yota had expected. Part of the problem was not being able to optimize the network before launch, Khachaturov said. The carrier is still optimizing the network and talking to carriers about how to boost performance.

Meanwhile, Yota is deploying LTE in many other cities across Russia that never had WiMax networks. It's providing 3G coverage elsewhere in the country through a partnership with another carrier, Megafon, which in turn has its customers roaming on Yota's 4G network. Yota offers wholesale services, so other carriers will also be able to use its network.