I actually tested this out myself in 2002. At the time, I was not trying to research 9/11 or anything like that. I was simply curious about whether or not cell phones actually work while you are flying. I guess it's part of my 'forbidden fruit' tendencies, but the fact that cell phones were prohibited across the board back then - between the time the captain decided that the plane was done taxiing and final take off preparations were to commence, until the plane had finished landing - I just had to try it and see what the deal was.

I flew from San Francisco to Miami. I kept my phone down at my side out of view of the stewardess and made constant attempts to connect during the entire flight, from takeoff to landing. while the plane was ascending I was able to make several successful calls until the plane was approximately 1000 to 2000 feet in altitude. At that point, a few calls connected but quickly cut out, and then for the rest of the flight, there were no bars whatsoever (until close to landing) - absolutely no signal. I even tried using the phone when I was passing over large cities, but still no signal. I tried making calls while the plane was descending to land, and was not able to successfully connect until it was down to about 2000 feet altitude approximately.

So, this was in spring 2002 or 2003. It was an American Airlines flight from San Francisco to Miami. That's all I remember.