Our power grids and communication grids are highly centralized. More so than most imagine.
I would guess that a large scale blackout of all wireless (and probably wired) communications in a specific geographic area would be the approach a panicky city or state government would use.
I have a relative who has been with Duke Power for 25 years and he told me recently that it frightens him how centralized the power grid is. Kind of like a Warner Bros cartoon where someone plugs in a hair dryer, blows a fuse and shuts down several states.
At the risk of sounding paranoid, I half think that the feds have been encouraging an over centralized power grid so they would have the capability of large scale blackouts in the event of significant civil disorder. OTOH, I have a friend that is far more plugged in to DHS & TSA and he thinks that it’s more incompetence than maliciousness. That was a while back, he may be rethinking that in light of the things that have been coming out more recently.
I wonder how suseptible our electric grid would be to a sustained attack by Iranian/Chinese/Russian “stuxnet” type or other sophisticated viruses?