I keep a POTS line, mainly as a fallback in case of storm damage. And, indeed, when my power failed here in Stamford during Isaias, the POTS line continued to work [but] the backup battery on my VOIP and Internet gave out.
I don't recall what the old standards for the CO backup power were, but I expected 24 hours - probably quite a bit more. Hah. Within about 8 hours, the POTS line was dead.
Now, it's certainly possible that this was independent line damage - but it was many hours after the storm itself passed, and there were no nearby line cuts in the area. (We had a large tree supported by communications lines leaning completely over a nearby road - but the POTS line came back when our power came back, several days before crews finally got to that tree.)
Of course, you only need to walk around the neighborhood a bit to see the sorry state of Frontier's external plant. Maintenance? Not a priority.
-- Jerry