Newly released documents show that for at least six years, drug agents have had near-immediate access to billions of phone call records dating back decades.
Officials have taken pains to keep the collaboration with Dallas-based AT&T secret.
The program, first reported Monday by The New York Times, is called the Hemisphere Project. It's paid for by the federal government, and it allows investigators armed with subpoenas to mine the company's vast database to help track down drug traffickers who frequently switch cellphones to avoid detection.
That's a different approach from that of the National Security Agency, which has come under fire for maintaining its own collections of call records.