Get help with TTY calls on Voice over LTE devices using iOS 8 and Verizon
When you make a TTY call from an iPhone 6 or iPhone 6 Plus using iOS 8 and Voice over LTE (VoLTE), you might not be able to send or receive TTY messages if one person on the call has a phone that isn't using VoLTE.
This article has been archived and is no longer updated by Apple.
When one of the phones isn't using Voice over LTE, TTY messages may transmit in only one direction. If both phones are using VoLTE, they can send and receive TTY messages normally.
To work around this issue, tap Settings > Cellular > Enable LTE and select Data Only. Then make the call again.