How to Turn Off TTY on the iPhone
Turning off the iPhone's TTY feature is easy and can be accomplished by completing a few simple steps.
If you see the TTY icon, which looks like a telephone receiver over a series of white dots , on the status bar at the top of your iPhone, the TTY feature is turned on. This feature, which is designed so hearing-impaired and speech-impaired people can conduct phone calls, can be turned off in the iPhone Settings.
Tap on the Settings icon on the home screen.
Scroll down the Settings screen and tap Phone.
Find the TTY button and slide it to the Off Position.
TTY stands forteletype. A separate TTY device -- which typically incorporates a keyboard and a screen -- is connected to the phones on both ends of a call for the parties to communicate. A TTY call differs from text messaging in that it is designed to be interactive back-and-forth communication just like a regular voice call. As one participant types a remark, it appears on the TTY device of the recipient, who can then type a response. Think of it as a phone call that is conducted by text.
TTY devices can be used both on landlines and on cell phones -- analog or digital. An adapter connects the iPhone to a TTY device.