How to Use iPhone's TTYby Danielle Gream
Teletype machines allow deaf and hearing-impaired individuals to communicate using on-screen text. Your Apple iPhone has TTY capabilities allowing it to be connected to a TTY machine via an iPhone TTY adapter, which is available for purchase from Apple. You can quickly prepare your iPhone for a TTY call using the Settings menu.
Tap "Settings" on your iPhone's home menu.
Scroll down and tap the "Phone" icon.
Move the TTY slider to the "On" position.
Connect your iPhone to your TTY machine using your iPhone TTY adapter.
Review the documentation that came with your TTY machine for device-specific instructions.