Just for the record: This was purely a communication exercise. The scenario was just an excuse to get people to talk to each other. Technical realism was not a goal in this exercise.
One can argue whether the assumptions on the availability of the PSTN was warranted or not, but given the fact that a good number of the involved teams had no direct contact prior to this exercise, this exercise was a worthwhile first step.
Do you suffer painful illumination? -- Isaac Newton, "Optics"