When I worked for Bluestar and Covad (old school DSL companies), we had a cage in the hosting center in Charlotte and Atlanta that was off-limits to our techs and even the telco techs. I always heard that it was the oft-rumored "black boxes" the government's supposed to have. Then a tech at the main POP in Atlanta told me one time that there's an entire floor there of un-touchable, government only "black boxes" that monitor phones and Internet for the entire Southeast.
I never really bought into all of it...but hmm...
Check these out -
AT&T tech outs NSA
AT&T forwards all Internet traffic to NSA
Google subpoenaed to turn over Gmail messages by FTC