I always have put my phone in air plane mode when i was in a train due to the modem consuming a lot more energy.
I always assumed and still doe its due switching towers and less connecitivy which means using more power.
Whenever people argue that public transport doesn't need wifi i would argue against it due to power usage and also for more accessablity of the internet in general.
[0] Phones
[1] The system which sits immediately behind cell towers and coordinates handoffs
[2] Tower
The cool solution would be base stations built into train carriages that then uplink through some kind of backhaul.
I think (but need to properly evaluate) that some Australian trains use something like this. EDIT: Nooope nope nope, horribly misread. https://goughlui.com/2014/03/23/random-post-railcorp-gsm-r-r...
As the essay notes, it's through TelephonyManager on Android. On iOS it used to be possible through CoreTelephony private APIs, but I think Apple cracked down on these a few years back and either removed them entirely or locked them down behind entitlements, as they were getting abused by analytics frameworks.
For example "Signal strength" APK. It's just matter of time until you will find one with logging and export ability. You can always write it down with pencil :)
What I don't get is why the author didn't draw the signal strength of all towers that were visible. This info is also trivially available.
What public transport needs are microcells, and to hell with wifi.