"Transport for London confirmed to the Guardian that 4G mobile
phone technology would go live in tunnels on most of the Jubilee
line from March 2020 and on other lines in the coming years."

https://www.theguardian.com/technolo...alling-at-all-
stations-tube-passengers-to-get-4g-reception-from-next-year

A spin-off from the 4g replacement for Airwave, it says. Which could
mean only EE customers will benefit. [Heigh ho, another reason for
getting a dual-SIM phone].
--
Roland Perry