What Does TTY Stand For?

TTY stands for Teletypewriter, sometimes called a text telephone. A TTY is a communication device that allows people who are deaf, hard of hearing, or speech-impaired to send and receive typed messages over standard telephone lines. You may also see TTY referred to as TDD (Telecommunications Device for the Deaf), though TTY is now the preferred term.

The telephone remains essential for daily tasks like scheduling appointments, contacting businesses, reaching emergency services, and staying connected with family and friends. For the millions of deaf and hard-of-hearing individuals in the United States, TTY technology has provided critical access to telephone communication since the 1960s.

What is a TTY Number?

A TTY number is a telephone number that connects to a TTY device rather than a standard voice phone. When you see "TTY:" followed by a phone number on business cards, government websites, or official documents, it indicates that the organization has a dedicated TTY line.

Many businesses, healthcare providers, and government agencies maintain separate TTY numbers to serve their deaf and hard-of-hearing customers directly. Federal agencies are required by law to provide TTY access. You may also see "V/TTY" listed after a number, which means that single line accepts both voice calls and TTY calls.
If you need to call a TTY number but do not have a TTY device, you can use the Telecommunications Relay Service by dialing 711.

How Does a TTY Device Work?

A TTY device consists of a keyboard for typing messages and a display screen or paper printout for reading incoming text. To make a call, the user places a standard telephone handset into the TTY's acoustic coupler, which converts typed characters into audio tones. These tones travel through the phone line and are decoded back into text by the receiving TTY device.

During a TTY conversation, both parties type their messages back and forth. The abbreviation "GA" (Go Ahead) signals when one person has finished typing and is waiting for a response. "SK" (Stop Keying) indicates the conversation is ending.
TTY devices use a communication protocol called Baudot code, which transmits at 45.5 baud (roughly 60 words per minute). Some modern TTY devices also support ASCII code, allowing communication with computers that have telecommunications capability.

What is TTY Mode on a Cell Phone?

Most smartphones include a TTY mode setting that allows the phone to communicate with TTY devices. When TTY mode is enabled, your cell phone can connect to an external TTY device through a headset jack adapter or specialized cable.
Cell phone TTY modes typically include three options. TTY Full mode transmits and receives text only. TTY HCO (Hearing Carry Over) lets you listen to the other party's voice while typing your responses. TTY VCO (Voice Carry Over) lets you speak while reading the other party's typed responses.

On iPhone, TTY settings are found under Settings > Accessibility > TTY. Android phones vary by manufacturer, but TTY options are generally located in the Phone app settings or Accessibility settings.

Many modern smartphones now support RTT (Real-Time Text), which provides a similar text-based calling experience without requiring a separate TTY device. RTT transmits each character as you type it, allowing for faster, more natural conversation flow than traditional TTY.

TTY vs TDD: What is the Difference?

TTY and TDD refer to the same device. TDD (Telecommunications Device for the Deaf) was the original term used when these devices first became available. Over time, the deaf community and industry shifted toward using TTY (Teletypewriter) as the standard term because it describes the technology rather than focusing on the user's hearing status.

You may encounter both terms interchangeably on older documentation, product packaging, and government forms. Some organizations still use "TDD/TTY" to ensure clarity for all users. When purchasing a device or looking up accessibility information, searching for either term will lead you to the same technology.

What is Telecommunications Relay Service?

Telecommunications Relay Service (TRS) allows TTY users to communicate with people who do not have TTY devices. When you place a relay call, a specially trained Communication Assistant (CA) serves as an intermediary between the TTY user and the hearing party.

The Communication Assistant reads the TTY user's typed messages aloud to the hearing party, then types the hearing party's spoken responses back to the TTY user. Relay services operate 24 hours a day, 7 days a week, with no restrictions on call length or number of calls.

To reach relay services from anywhere in the United States, dial 711. This universal number automatically connects you to your state's relay service. You can also find your state's direct toll-free relay number in our Relay Service Directory.

Relay services are free to use and are funded through a small surcharge on telephone bills, as mandated by the Americans with Disabilities Act.

Types of TTY Devices

Several types of TTY devices are available to meet different communication needs and preferences.

Traditional TTY machines feature a full keyboard, display screen, and acoustic coupler. These desktop devices offer reliable performance for home or office use. Models like the Superprint 4425 include additional features like ASCII compatibility for computer communication.

Portable TTY devices provide compact, travel-friendly options for users who need TTY access away from home. These lightweight units can connect to any standard telephone line.

Captioned telephones represent a newer technology that displays real-time captions of what the other party is saying during a voice call. Unlike traditional TTY, captioned phones allow hard-of-hearing users to speak and listen while reading captions for clarity. These devices are popular among people with partial hearing loss who can still use their voice.

Is TTY Still Used Today?

While newer technologies like video relay service (VRS), IP Relay, and RTT have expanded communication options for the deaf community, TTY remains an important and widely used technology. Many people prefer TTY for its reliability, simplicity, and compatibility with standard phone lines.

TTY is particularly valuable in situations where internet access is unavailable or unreliable, during emergencies when cell networks are congested, and for users who are comfortable with the technology they have used for years.

Government agencies, hospitals, emergency services, and businesses continue to maintain TTY lines to ensure accessibility for all callers. The Americans with Disabilities Act requires certain entities to provide TTY access.

TTY Terminology Glossary

TTY (Teletypewriter) - A device that allows text-based communication over telephone lines. Also known as TDD (Telecommunications Device for the Deaf) or text telephone.
TDD (Telecommunications Device for the Deaf) - The original term for TTY devices, now less commonly used.
Baudot Code - The standard communication protocol used by TTY devices, transmitting at 45.5 baud.
ASCII - American Standard Code for Information Interchange, a computer communication code. Some TTY devices support ASCII for computer compatibility.
VCO (Voice Carry Over) - A relay service option where the user speaks directly to the other party and reads typed responses. Useful for people who can speak clearly but have difficulty hearing.
HCO (Hearing Carry Over) - A relay service option where the user listens to the other party and types responses. Useful for people who can hear but have difficulty speaking.
GA (Go Ahead) - TTY abbreviation signaling you have finished typing and are waiting for a response.
SK (Stop Keying) - TTY abbreviation indicating the conversation is ending.
Auto ID - A TTY feature that automatically transmits an audible tone to identify incoming TTY calls. Especially helpful in emergency situations.
Turbo Code - A TTY feature that increases transmission speed for faster communication.
Acoustic Coupler - The component of a TTY device that holds the telephone handset and converts electrical signals to audio tones.

Shop TTY Devices and Captioned Phones

ADCO Hearing Products specializes in communication solutions for the deaf and hard of hearing, including TTY devices and captioned telephones.

If you're looking for TTY (Teletypewriter/TDD) options, captioned phones, or related assistive devices to improve your phone communication, our product specialists are here to help. We can guide you through available models and features (such as amplification, large displays, or compatibility) to help you find the right fit for your needs.

What is TTY?