This 1976 short film, called called The Twins, was released in 1976 by Western Electric about the AT&T switching system at the World Trade Center. The narrator declares: "Before a skyscraper goes up, it's got to go down. For the World Trade Center they first dug out 14 acres of Lower Manhattan, and carried it over to the Hudson River, creating six new blocks of real estate."
The company posted the video recently, writing, "After 9/11, it was reported that one of the few things to survive the WTC attacks was AT&T's switching system. 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."
Check it out below (there's a vertigo-inducing shot at the 1:19 mark):
[via Laughing Squid]