The Pay Phone Shelf-Top TTY is a telecommunications device for the deaf (TDD) designed to work with any public telephone. This device works with most types of public telephones and popular enclosures, and has no affect on the use of the telephone by the hearing public. Designed for use in public areas and buildings where vandalism is not a concern, the unit is designed to be connected accousically to the pay phone or installed by a professional installer for direct connection; the unit is intended for mounting on the enclosure shelf below the existing phone. Standard features include Turbo Code, TTY Voice Announcer, a one-line 20-charachter vacuum fluorescent display, conversation memory that clears when the call is disconnected, arrow keys, call progress indicator, and an on-line help menu. TELECOMMUNICATIONS: Baudot (TDD standard) code at 45.5 baud; international (50 baud) code; Bell 103 or ASCII optional. POWER: Transformer input, 115 VAC, 1.0 A (max); transformer output, 12 VAC, 72 VA (max). WARRANTY: On year limited.