47 CFR 42.6: Retention of telephone toll records.

Each carrier that offers or bills toll telephone service shall retain for a period of 18 months such records as are necessary to provide the following billing information about telephone toll calls: the name, address, and telephone number of the caller, telephone number called, date, time and length of the call. Each carrier shall retain this information for toll calls that it bills whether it is billing its own toll service customers for toll calls or billing customers for another carrier.