A short film about the building of the World Trade Center AND the telephony challenges the construction posed. The Bell System had installed a #1ESS Western Electric central office switching system within the towers. There are plenty of shots of the Towers being built, and then filled by companies, back in the 1970s.
After 9/11, it was reported that one of the few things to survive the WTC attacks was AT&T's switching system, which was good because many people relied on the mainframe for their telephone connectivity. AT&T's local network switching equipment that routes telephone calls was located in a deep sub-basement of the Towers and somehow survived the collapse of the buildings. None of AT&T's employees were hurt in the attacks.
Footage courtesy of AT&T Archives and History Center, Warren, NJ