The article states that Atta called Al-Shehhi on a cell phone while waiting to take off. I wonder if there is any evidence of phone calls from any of the known hijackers to terrorists who have been rumored to have been on other planes, their plans thwarted by the quick decision to ground all planes.
The trip(s) to Bangkok are of possible interest. Recall the speculation that the anthrax might have come from Southeast Asia.