[OneWingedShark]

They’re not smart enough to shut all comm down at once.

Cutting power and land phone would be 70% of the comms, bring in cell-jammers (or cut power to the towers as well) and that's 95%.
That's doable, and not exactly hard to coordinate.

We’ll know something is amiss, sufficient to be on guard.

Perhaps.

The shutdown would have the effect of limiting coordinated defense.

Not necessarily, military comms especially operates on self-supplied power (be it battery or generator) and a different portion of the EM spectrum.

[G Larry]

I meant we citizens defending against Obamunism.