Facility Telecommunications Management for the Government Emergency Telecommunications Service [open pdf - 313KB]
From the Introduction: "This document provides telecommunications management information for organizations that use the Government Emergency Telecommunications Service (GETS). It identifies information on obtaining basic facility access to GETS, and optional steps that may be taken to improve GETS access. The GETS capability is based in the public wireline telephone networks, also known as the Public Switched Telephone Network (PSTN)."
U.S. Department of Homeland Security: https://www.dhs.gov/