As far as the old Bell System went: if you look, the old CO buildings have big parking lots around them (sometimes on all sides, and fenced off; other times actual parking lots on one or two sides. Those used to have huge diesel tanks in them (dunno if they still do this). The basements of those buildings we full of -48V batteries (dealing with H2 outgassing was an engineering issue). IIRC they were supposed to have a week's capacity, though that seems implausible to me.
Our current system is more capable but much less resilient.
I used to regularly lose landline service after storms (further north on the East Coast). For a while, I had both a landline and a cell phone, and found myself with the oddity of calling the phone company on my cell phone to tell them that my phone didn't work.
(I still technically have a land line. It comes free with the fiber optic data line. But there are no phones connected to it. At one point I discovered that it had been down for months, and didn't care.)