"AT&T's 1.9-Trillion-Call Database"
This whole article is worth reading, but I found this tidbit particularly interesting:
He was alluding to databases maintained at an AT&T data center in Kansas, which now contain electronic records of 1.92 trillion telephone calls, going back decades. The Electronic Frontier Foundation, a digital-rights advocacy group, has asserted in a lawsuit that the AT&T Daytona system, a giant storehouse of calling records and Internet message routing information, was the foundation of the N.S.A.'s effort to mine telephone records without a warrant.
An AT&T spokeswoman said the company would not comment on the claim, or generally on matters of national security or customer privacy."