Good idea. Cell sites are battery backed up as well, FYI. BUT they go dead very quickly. Might not have cell phone service with prolonged power outages..
In Norway they have in their great wisdom of course replaced all switchboards with digital ones, without any software. The software is placed in a central, so when you power up the switchboard it goes to an IP address, and downloads the software. If this was in the US, it would be like the phone line between Nevada and California broke, all citizens in California would be without telephone service since the software was on a server in Washington DC. Isn't that a wonderful way of doing it ?
Being educated in modern digital automation I have come to hate it. Not that it could not work, but someone just had to start cutting corners, everywhere. And that is when I started hating modern technology. Get me the landline back, and a crank on the phone, or at least the rotary phone with pulse technology.
Bill