I worked in a downtown Dallas office building in those days. My 7th floor office window, on a clear day, commanded a look of the flat, indistinctive North Texas landscape that was so broad and distant that one could almost make out where the Earth's surface made its subtle curve toward the other side of the planet. However, on most days the smog and ozone cleared only enough to reveal the lower parking levels of a nearby office building. So instead of marveling at natural wonders, a few of the IT people I shared the floor with would occasionally entertain ourselves by trying to identify which airline's planes from the multiple airports nearby were the ones rattling our windows at any given moment.
I came into the office a little earlier than normal that Tuesday morning, still a bit hung over from the previous week's annual sand, surf and suds vacation with friends, and logged into my computer. That's where I first saw the bulletin about a plane striking one of the Twin Towers.