I too question how things are going
My local EE mast goes down in power cut and I am assuming it has no form of backup, will it ever even with ESN being rolled out?
Voda/O2 stays online as the mast has batteries, not sure for how long as not had long enough outage locally but not being optimistic on time
My FTTP and FVA phone is reliant on ONT batteries and UPS for outage
FTTC is not powered centrally from an exchange with large backup or generator so wont last for more than max of 8 hours, Sometimes power can go down to a local cabinet and an end user does not have a power outage a mile or so away which can also be a pain.
Digital IP voice will be reliant on UPS and generator for long term outage to power the equipment for the IP connection.
In my opinion things have taken a decline in level of continuity and reliability, Which will have an impact of when we will need modern technology most,
this will leave us in the dark and cut off at some point in the future not just for emergency services but communications to each other, in a national power outage such as 9th August 2019 which affected allot of the UK and communications. One would of hoped things could have been learnt from that day.
Satellite is an option but depends on if you are concerned with latency.
DS Forum link Outage of Mobile Comms.
Power outage lessons article