The problem not addressed is dial tone. I know a guy who lived in New York during one of their long power outtages years ago. No one could get a dial tone on their cell or landline. He said people were going in public buildings with their cell phones on as flashlights so they could find payphones -- payphones worked, but you had to have quarters or some other way of paying for the call, and your calls to local numbers probably wouldn't go through. Long distance calls did, though.

When a disaster happens, everyone tries to get on the phone and make a call, so it doesn't matter if the phones are "working."