RTT (Real-Time Text) is a communication feature available on iPhones that allows users to send and receive text messages in real-time during a phone call. It is primarily designed for individuals with hearing or speech impairments, as it enables them to have text-based conversations in real-time without relying solely on voice communication. Here’s how you can use RTT on an iPhone:

1. Enable RTT: Go to the “Settings” app on your iPhone.
2. Scroll down and tap on “Accessibility.”
3. In the Accessibility settings, tap on “RTT/TTY.”
4. Enable RTT/TTY by toggling the switch to the “On” position.
5. Start a Call: Make or receive a phone call as you normally would.
6. Switch to RTT: During an active phone call, you’ll see a new button labeled “RTT” in the in-call controls. Tap on the “RTT” button to switch to the RTT mode.
7. Type and Send Messages: Once you’re in RTT mode, you’ll see a text entry field where you can type your messages. As you type, your messages will be sent in real-time to the other person on the call.
8. Read Incoming Messages: Messages sent by the other person will appear in the chat view, allowing you to read them as they are received.
9. End the Call: When you’re finished with the call, tap the “End Call” button to hang up.

Using RTT on an iPhone allows for more accessible communication during phone calls, particularly for those with hearing or speech impairments. Both participants need to have a device that supports RTT for it to work effectively.

Please note that RTT is a carrier-dependent feature, so it may not be available on all iPhone models or with all mobile network providers. Additionally, standard voice calling charges may apply when using RTT, depending on your phone plan.