A TTY (teletypewriter) is a device that lets people who are deaf, hard of hearing, or speech-impaired make phone calls by typing text instead of speaking. Each person in the conversation types on a keyboard, and the messages appear on a small screen. TTY devices have been a communication lifeline since the 1960s, though they’re now being replaced by newer text technologies built into smartphones.
How a TTY Works
A TTY looks like a small keyboard with a display screen. When you type a message, the device converts each letter into electronic signals (audible as a series of beeps) that travel through the phone line. The TTY on the other end receives those signals and converts them back into letters on its screen. Both people need a TTY, or one person needs to use a relay service, for the call to work.
Traditional TTY devices connect to a standard landline, either by plugging directly into the phone jack or through an acoustic coupler that sits over the handset. The technology was invented in 1964 by Robert Weitbrecht, a deaf physicist, and it remained the primary way deaf and hard-of-hearing people used the telephone for decades.
TTY conversations have their own shorthand. “GA” means “go ahead,” signaling that you’ve finished typing and it’s the other person’s turn. “SK” means “stop keying,” indicating you’re ready to end the call. “SKSK” means you’re hanging up. These abbreviations keep the back-and-forth flowing since both parties can’t type simultaneously on older TTY systems.
Relay Services and 711
Most phone calls involve someone on the other end who doesn’t have a TTY. That’s where telecommunications relay services (TRS) come in. You dial 711, which connects you to a relay operator. The operator reads your typed messages aloud to the hearing person and types their spoken responses back to you. The FCC requires all businesses, government agencies, and nonprofits to accept relay calls and treat them the same as any other phone call.
Relay services also offer specialized modes for people with different combinations of hearing and speech ability. Voice Carry-Over (VCO) is for people who can speak but can’t hear: you talk directly to the other person, and the relay operator types their responses back to your screen. Hearing Carry-Over (HCO) works the opposite way, for people who can hear but have difficulty speaking: you type your part of the conversation, the operator reads it aloud, and you listen to the other person’s reply through the handset.
Legal Requirements Under the ADA
The Americans with Disabilities Act requires state and local governments, businesses, and nonprofits to communicate effectively with people who have hearing or speech disabilities. TTY access is one of the recognized tools for meeting this obligation. Covered organizations must provide auxiliary aids like text telephones, captioned telephones, or videophones when needed. They’re also required to accept calls placed through relay services, meaning staff who answer the phone cannot hang up on or refuse a relay call.
TTY on Smartphones
You don’t need a standalone device to use TTY anymore. Both iPhones and Android phones have built-in software TTY and RTT modes in their accessibility settings. On an iPhone, you go to Settings, then Accessibility, then RTT/TTY to turn it on. Once enabled, you can make and receive TTY calls directly from the Phone app without any extra hardware. A small TTY icon appears in your status bar when it’s active.
Your carrier determines whether you see options for RTT, TTY, or both. You can also choose whether to send text character by character as you type or wait until you’ve composed a complete message. If you prefer to use a physical TTY device, there’s a “Hardware TTY” toggle that routes calls through an external device connected to your phone.
The Shift From TTY to Real-Time Text
TTY was designed for old landline networks, and it doesn’t work well on modern internet-based phone systems. The signals degrade, calls drop, and the technology can’t keep up with how people communicate today. In 2016, the FCC adopted rules allowing wireless carriers and phone manufacturers to support Real-Time Text (RTT) as a replacement, with a phased rollout that ran through 2021.
RTT improves on TTY in several meaningful ways. Text appears on the other person’s screen as you type each character, not after you hit send. This creates a more natural, conversational flow similar to a voice call. RTT also lets you send text and voice simultaneously on the same call, so you can type part of a message and speak part of it. It supports international character sets, has built-in error detection for lost data, and avoids the out-of-order message problems that plague regular texting.
Because RTT is built into modern smartphones as a native feature, it doesn’t require specialized equipment. It works over the same internet-based networks your phone already uses for calls. The FCC initially required RTT to remain compatible with older TTY devices on other networks, though that backward-compatibility requirement is being phased out as TTY usage declines.
For anyone still using a traditional TTY, the device continues to work on landlines. But for most people, the combination of smartphone RTT, video relay services, and captioned calling apps has made the standalone TTY device largely a thing of the past.