> 1 | Introduction

> This document describes the technical requirements for using a TTY device. Your GSM engine offers basic support for equipment using the CTM standard (Cellular Text Telephone Modems). TTY stands for Text Telephone and is a special device that lets people who are deaf, hard of hearing or speech-impaired use telephone systems to communicate via PSTN. A TTY is a special device that allows users to type messages back and forth to one other.
> It is required at both ends of the conversation in order to communicate.