I am not a structural engineer either, but I do remember all of the cell phone calls reportedly made from the hijacked planes. These planes were not low enough to make the calls that reportedly went through. The technology for calls above 8000 feet did not exist yet. Please read the following analysis of the heights of the undisputed altitudes of the planes and the reported times of the cell calls:
http://www.globalresearch.ca/articles/CHO408B.html