I was still working 3p-12am at the time so I was sound asleep when my boss called my cell phone and told me that we were under attack. The fog hadn't cleared and so I'm just like "Dude, what are you talking about? Who is attacking? And who's under attack?" He told me the US was under attack and to turn the TV on. I remember asking what station and he said any station. The first thing I saw was the 2nd plane hitting the tower. It was a replay as it had happened a few minutes prior and the newscasters were still trying to take in what they had just seen.
Was told that we were going to be open for work but that security was going to be extra tight and to make sure to wear my badge visibly on the way to work. The loop (635 in Dallas) was the emptiest I ever saw it that day. It was just so eerily quiet everywhere. People at work were afraid that we were going to be a target, a fear I didn't share, but I understood the fear. Everyone was in tears or in shock at the call center.
We were receiving calls from up in the NE about internet not working and it had been said that some of the major trunks we used were under the WTC and was completely inaccessible so there was nothing we could do. Most people that called in understood but I'll never forget the call one of my coworkers got - it was from another New Yorker and he was pissed that his internet wasn't working. He explained the situation to the customer but the guy said something to the effect of not caring about towers and a bunch of dead assholes - he just wanted working internet. And he was promptly hung up on.