But where I live there's a big hill between me and the nearest cellphone tower; in fact reception is very patchy for a mile or so all around. If the broadband went down I'd be completely cut off. (My phone and my internet are both with BT.)

Not all cellphone towers work well across all networks. Here where I am O2 and Vodaphone don't have a good signal even when in sight of the tower, but EE and 3 are excellent. Ask neighbours and friends who they are with and their signal quality. You may need to change your provider.

Joe

One major issue is if your broadband goes down so does the phone. No emergency calls.

Should the broadband go down, BT presently have a Smart Hub2 system that will auto switch the router via a sim to the mobile network to maintain broadband. If that is issued to every broadband installation it would alleviate a lot of issues.

But where I live there's a big hill between me and the nearest cellphone tower; in fact reception is very patchy for a mile or so all around. If the broadband went down I'd be completely cut off. (My phone and my internet are both with BT.)

Should the broadband go down, BT presently have a Smart Hub2 system that will auto switch the router via a sim to the mobile network to maintain broadband. If that is issued to every broadband installation it would alleviate a lot of issues.

All this technological advancement is all very well and convenient, and I use it - mainly because there is no option, but I don't know, somehow the 'instant-on', 'instant communication', 'instant gratification', 'Instant Information', 'tap'n'go' the supercalifragilisticexpialidociousness of it all seem to drain something out of life.

E. M. Forsters 'The Machine Stops' (1909) seems to be where we are heading. Well worth reading or listening to:
https://www.youtube.com/watch?v=ZOr-jb6ElzE

And no, the irony of providing the link is not lost on me, but what can you do?

https://www.bt.com/broadband/digital-voice

Joe