iPhone used for TTY or Relay calls

[ImNotADweeb]

Hello! I just want to ask if some of you guys have experienced making calls to TTY or Relay calls? My friend is deaf and she doesn't know how to use an iPhone for making video, text relay calls. If I am a little more informed about this then I'd surely recommend iPhone to her. Any infos on the app, whether it should be installed on an iPhone or use the browser in accessing the relay website, will be very much appreciated.