I'm surprised there are more conspiracies about this than the facades you can find walking around Manhattan. I remember stumbling upon one without knowing what they were, and being rather confused (and suspicious).
This AT&T building is a pretty cool piece of mysterious brutalist architecture. It's noticable and leads to wonder about what's inside. And infamous because it was (is?) home to an NSA monitoring installation exposed in some leaks.
It was also featured in media like the Mr Robot series.
Not to say that the AT&T building isn't creepy - I've walked by it a few times and it always made me laugh a little at how ridiculously evil it looks.
[1] https://roadtrippers.com/magazine/new-york-fake-facades/