In NYC
Being at an adjacent office space of a trading floor, we watched the plane hit on monitors.
If you know about satellite trading desks, they rely on 'Squak Boxes' to communicate. Direct links without phone lines.
The traders on the other end said they think they felt the building move.
We advised them to exit the building as soon as possible, and we implemented our Crisis Management Disaster Recovery Plan, evacuating buildings across the country in metropolitan areas. (Boston, Atlanta, Chicago, etc)
In NY we had contracted with ferry services as part of our plan to shuttle employees to NJ and our recovery centers for critical staff, and private bus services to take employees home for non-critical staff.
By late that afternoon all major banks were operational at their recovery centers.