Room 641A at 611 Folsom Street

Wired has the former At&T technician Mark Klein's evidence on the NSA wiretapping program

In 2003 AT&T built "secret rooms" hidden deep in the bowels of its central offices in various cities, housing computer gear for a government spy operation which taps into the company's popular WorldNet service and the entire internet. These installations enable the government to look at every individual message on the internet and analyze exactly what people are doing. Documents showing the hardwire installation in San Francisco suggest that there are similar locations being installed in numerous other cities.
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In San Francisco the "secret room" is Room 641A at 611 Folsom Street, the site of a large SBC phone building, three floors of which are occupied by AT&T. High-speed fiber-optic circuits come in on the 8th floor and run down to the 7th floor where they connect to routers for AT&T's WorldNet service, part of the latter's vital "Common Backbone." In order to snoop on these circuits, a special cabinet was installed and cabled to the "secret room" on the 6th floor to monitor the information going through the circuits. (The location code of the cabinet is 070177.04, which denotes the 7th floor, aisle 177 and bay 04.) The "secret room" itself is roughly 24-by-48 feet, containing perhaps a dozen cabinets including such equipment as Sun servers and two Juniper routers, plus an industrial-size air conditioner.

The movie they make about this in the future needs to be called: Room 641A.