TDD/TTY : A device that is used in conjunction with a telephone to communicate with persons who are deaf, who are hard of hearing, or who have speech impairments, by typing and reading text
NFPA 1221 Standard for the Installation, Maintenance, and Use of Emergency Services Communications Systems, 2007 ed. (Std: Install, Maint, and Use of Emr Srvc Commun - Amer) {391 NFC}