Once again, I suggest everyone interested read James Bamford's book Shadow Factory. All these revelations regarding call metadata, PRISM collection (albeit under a different codename at the time), modern fiber taps, and even more are covered. You'll learn about how they shave fiber optic cables in order to intercept traffic and not be detected. You'll find out about the various facilities already reported, along with…
In any case, it's wildly interesting stuff.