At the time, I was working at Verizon in a Major Customer Care Center, we were responsible for anything from a plain phone line all the way up to a T3 for major customers (think top 100), Federal Government, state, county and local government for MD, DC, VA, and WV. We got the news of the first flight and, like everyone else, thought a small plane. Turned on a TV to see the 2nd plane hit the tower. Shortly thereafter, all hell broke lose for us when the 3rd plane hit the Pentagon, half a side away from our Central Office in the Pentagon. On the Maintenance side, my crew was responsible for .gov and .mil customer. I had two guys dedicated to working with the Pentagon central office to keep everything up, even while the guys at the pentagon kept sandbagging the door to keep the water out that started to flow in from the fire operations. The Central office never went down and was never overwhelmed by water (6 foot sandbag and trash wall helped), and the worst outage we had a fax line to the loading dock on the far side of the building. I had one of my testers go home do to not being able to contact a very close friend that worked at the Pentagon, it was later discovered that the plane had pretty much come through the window of her office and she never had a chance.
We were also tasked with supplying 96 phone line in less than 4 hours to a hotel conference center out by Dulles airport as an information hotline for American Airlines with regards to flight 77 out of Dulles.