My wife & I were living and working in Canton, OH at that time. My sister and her 1 year old were staying with us at that time. The company HQ was in Houston at that time in a tall building. They evacuated everyone from the building and sent them home.
I was at a combined training class and troubleshooting seminar in Houston, in a hotel conference room in Greenway Plaza. Everyone's pagers started going off right after a guy at the training class burst into the conference room returning from an unscheduled restroom break hollering "It's war! They're flying airplanes into buildings!" We saw the impact of the second plane on a TV the hotel personnel had set up in a common area adjacent to the conference rooms.
I was able to fly back that Fri, several hours later than my flight was initially scheduled. Intercontinental Bush was swarming with soldiers, Texas Highway Patrol, Border Patrol, all sorts of armed and ready eagle-eyed folks drawn from as many places as they could. My wife was also able to return that Friday, flying back from Indianapolis.
We learned United Airlines flight 93 had passed either very close to or over our house before crashing in Pennsylvania.