The story AT&T is pushing -- starting about 16 hours following the outage's start -- was that it was a failed software update.

And as much as I like a good conspiracy theory, this actually tracks.

Why?

Because my Microcell device (basically a tiny cell tower in my house which only covers the house itself, and uses the internet for calls) went to 0 bars right when the regular towers did.

An attack on the towers themselves would not have affected my Microcell, which basically just emulates what the towers do.

I theorized that this had to be a situation where all AT&T transmissions were either corrupt or modified in some way, to where the cell phones couldn't see them anymore. And it looks like that's exactly what happened. An erroneous software update caused the towers and Microcell devices to send out a signal which the phones could not understand. Hence, you abruptly went to 0 bars and it was like the towers were all suddenly missing.