Mobile phone coverage coming to the London Underground tunnels

Mobile phone coverage is to be extended to the entire London Underground following successful trials along the Jubilee line extension.
At the moment, there is WiFi coverage in the stations, available to all mobile networks except Vodafone, but cellular coverage is limited to surface areas and a few shallow underground stations that accidentally get it due to their design.
To improve phone coverage in the Underground, a trial of adding mobile phone coverage in tunnels and stations started last ye