A whistleblower talks to Wired about the secret room at AT&T where call data is forward to the NSA.

Meanwhile, Seymour Hersh has a pretty sensible guess as to how the whole NSA wiretapping thing works:

The N.S.A. also programmed computers to map the connections between telephone numbers in the United States and suspect numbers abroad, sometimes focussing on a geographic area, rather than on a specific person — for example, a region of Pakistan. Such calls often triggered a process, known as “chaining,” in which subsequent calls to and from the American number were monitored and linked.

The way it worked, one high-level Bush Administration intelligence official told me, was for the agency “to take the first number out to two, three, or more levels of separation, and see if one of them comes back” — if, say, someone down the chain was also calling the original, suspect number. As the chain grew longer, more and more Americans inevitably were drawn in.

….The point, obviously, was to identify terrorists. “After you hit something, you have to figure out what to do with it,” the Administration intelligence official told me. The next step, theoretically, could have been to get a suspect’s name and go to the FISA court for a warrant to listen in….Instead, the N.S.A. began, in some cases, to eavesdrop on callers (often using computers to listen for key words) or to investigate them using traditional police methods. A government consultant told me that tens of thousands of Americans had had their calls monitored in one way or the other.