A couple of things people aren't mentioning here.
When a natural disaster occurs and power is disrupted the legacy POTS line is "often" not impacted. As a telco engineer we saw the benefits of this during both Christchurch Earthquakes.
There is no government requirement (as far as I know) for a mandatory off-mains up-time for a cell site. Battery upgrade programs are incredibly expensive, and with stable mains networks can often be deferred for more important maintenance. During the Canterbury earthquake some standby generators deployed to critical cellular sites went "missing" soon after being set up. Cellular has it's limitations - especially when idiots set fire to them.
When troubles come, as they invariably do - you'll be much better off with a legacy POTs service and a roll of cash hidden in the house. Plastic without EFTPOS has no value.
Personally - I'm still on VDSL and POT's line due to my older monitored alarm which will not work over SIP. Yes - I know about options for older panels but as soon as I pay to migrate the panel, my monitoring costs double as well.
Frankly until I absolutely have to, I'll stay on copper.
Just my 20 cents
- These thoughts are my own and are in no way, shape, or form, necessarily those of my employer :)