And if the disaster is an Electromagnetic Pulse?

[Lightspeed]

You could have a point there BP

Run up and immediate aftermath use cell network to control population and to herd them / make them stay put as required.

This will PERHAPS give time for marshal law type procedures to be activated ( I don't see how though), and at that point cell network will lock out all but Mil and gov coms.

This would be a smart trick....get the general population to rely 100% on information and instruction received their mobiles, and once reliant and in the desired location / physical condition, to withdraw that service.