Perhaps, perhaps not. I live in Ontario Canada and in the recent blackout, my phone kept working.
i.e., you did not have a ISDN or wireless phone
The telco can provide power over the ISDN line for a single device on the ISDN bus if that device can operate under the necessary restrictions. (This power is so limited that it takes several seconds for the phone to become operational in emergency power mode.)
But what good does it do to have DC on your phone line if the network is utterly congested? With IP the service level degrades more gracefully. (Although this wouldn't necessarily work well for _voice_ over IP.)