Dozens, if not hundreds, in every major US city at the very least. Have we really not learned anything in the recent years, that we're still unsure about such basic questions? Imagine the KGB at its peak activity, bump it up by a few orders of magnitude, and you have the NSA. Man, despite everything, the US is still really good at brainwashing even its most tech savvy citizens.
> I'm surprised we haven't had many more leaks about them given what I would consider the ease of identifying them
I think you're greatly overestimating "the easy of identifying them", and how much the average AT&T employee knows/cares. Things are also probably much better hidden now compared to 2006.