The one-page document from the Justice Department's cybercrime division shows, for instance, that Verizon Wireless keeps, for a year, information about which cell towers subscriber phones connect to. That data that can be used to figure out where the phone has been, down to the level of a neighborhood. AT&T has kept the same data continuously since July 2008.
The sheet is a guide for law enforcement, which can request the information from the carriers through legal channels. The ACLU obtained it through a Freedom of Information Act request.