What happens when Aimee tries to call her mother early on September 11?

Aimee tries to call her mother early on September 11. At first the phone rings and rings and rings, and then finally her mother picks up. They chat for a few moments, and then her mother says that she needs to get to her meeting at the World Trade Center. She starts to get into a cab while she is talking to Aimee. Then she changes her mind, and she tells Aimee she will talk to her in the lobby and skip her meeting.