Switch TTY/TDD mode on to make calls with a TTY/TDD device. These devices are for the speech or hearing impaired.

  1. On the start screen, swipe left, and tap settings iconSettings.
  2. Tap ease of access.
  3. Under TTY/TDD mode, tap Full.

    The available modes may vary depending on your network service provider.

    For more info on using your phone with a TTY/TDD, go to http://www.microsoft.com/windowsphone/en-gb/howto/wp7/basics/use-my-phone-with-a-tty.aspx.