I heard the same "small commuter plane" thing from my Digital Pager (ha) news alerts.
I thought that sounded strange and turned on CNN in time to see the second plane hit.
I also went to a customer to do training (in Nashville, TN), but when I arrived, their doors were locked. I knocked and someone inside peeked out. They opened the door, I explained why I was there and they said they had sent all the employees home.
I had a friend who worked in WTC Building 7. He decided to call in sick on 9/11, but he wasn't sick.