My Dad was a 45 year Telco worker who started out replacing old crank magenta phones with rotary ones back in the late 1940's. From there here became a central office repairman in the long distance switching office called 4A. When it went to Electronic Switching in 1980 he went back outside and maintained data circuits including 911 center until retirement in about 1993 or so.
Landlines are or rather used to be until AT&T stopped maintenance the most reliable phone service. If maintained properly it still would be. Cell service will never reach landline reliability for several reasons most of which is being done by cell companies. Cell companies will not build a true nationwide grid of towers. They put them up in more densely populated areas and along the interstate system. In states from Maine going southwestward to northern Alabama meaning the Appalachian, Cumberland, Blue Ridge etc mountain ranges and foothills is very hit and miss in service.
I guarantee you if you buy a cellphone you will see yet another generation replacing it within five years and no additional towers in outlying areas added. Meaning what you knew as 3G, 4G, 5G, and now planning for 6g and still no true national cell grid. The higher the frequency spectrum the lower the coverage area UNLESS more towers are put up closer together. My 3 G worked most of the time at my home. 4G was very hit and miss and except in dead of winter with no leaves 5G is impossible. So I use WIFI calling through my VIASAT satellite internet system. It works better than the cell towers but has its own issues.
I lost my landline for good about 4 years ago. Tree's would fall on the ariel line serving my road which is a quarter mile long and 4 houses. The first time it happened they came out and ran about 100 ft of drop wire on the ground to connect two pole spans of line. They left the cable on the ground and the splices unprotected. Each time it rained I lost service. I'd call it in and not get past the automated system who said someone would be dispatched because it saw trouble on the line. Before dispatching maybe a week later it tested it again and if the line was dry did not dispatch and ZERO human interaction. Finally after another tree fell and cut the line again they never came back. If my Dad had left a mess like what was done on my road he would have been fired. Ma Bell had it's issues and he even took his employer to the state Public Service Commission to get buried cable to replace the old rural paper insulated ariel lines. That was in 1978 when he was at South Central Bell aka Bellsouth.
When Judge Green who ordered the AT& T split that in turn destroyed AT&T reliability, they bought back all their previous Bell system companies they were split from, then more. They eventually laid off or forced retired about 90% of their entire technicians each time they bought a former asset back.
For those who don't understand AT&T used to be the parent company of most phone companies which operated as The Bell System under different regional names, as well as Western Electric. I have not seen an AT&T van nor truck in Knoxville, TN area in over a year.
The one company who has come the nearest to putting a true national grid in place is SpaceX if they also go cell but at least it can work inside the home of WIFI. The cell companies just like the Cable companies are going to continue cherry picking areas and call it coverage. COMCAST BTW wanted $15K to run service on my road. I do live in a rural area but they came up the main road and cherry picked the ones there likely while using Rural Interne=net connecting funding. As a nation we need reliable communication and up until about 15 years ago we had it. Not any longer.
Re: 66 - As long as copper lines are available, we will use them for specific applications.
911 is a good example. We have not had good luck with 911 trunks over fiber when power goes out. The fiber mux needs power, etc.
Any day I can rely on tip and ring, I will do so until that is not available. All trunks in our 911 loop are currently copper.
A dated data point but in the 2003 Power Blackout, at least in these parts the cell phone service simply could not handle the load. Land lines fared better. Yes, you could still get a reorder, but by and large, calls could be completed.
Obviously there have been improvements in cellular infrastructure and carriers such as ATT offer their FirstNet service that provides preemption for First Responders, IT, etc. My guess is that the outside copper plant has been so poorly maintained in the last 20 years that a similar power outage in 2024 would expose more gaps where copper once ruled.