I listened to some of these on the radio, on the way to work this AM:
the NORAD folks just couldn't seem to grasp that this was NOT a "drill" - right up until the first plane hit the WTC.
Heard this goofy woman saying, "A plane's been hijacked?
Cool!"
Wanted to reach into the radio, and back in time, and just grab her by the throat!
I read somewhere that NORAD was, in fact, having hijacking drills that very morning. I'll try to remember where I read that.
Some conspiracy types were saying that the drills that morning were part of the setup in order to delay any quick reaction by any air defense units.