Zte Z716BL User Manual page 58

 TTY Off: Users who can hear and talk can disable TTY
support.

TTY Full: Users who cannot talk or hear may use this
mode to send and receive text messages through a TTY
device.

TTY HCO: Users who can hear, but cannot talk, may use
this mode to listen to conversation of the other party and
respond via text messages.

TTY VCO: Users who can talk, but cannot hear, may use
this mode to talk through the phone and receive
responses via text messages.
Set DTMF Tones
You can set the length of Dual-tone multi-frequency (DTMF)
signal tones.
1. Touch the Home key >
Settings > Call settings > DTMF tones.
2. Touch Normal or Long.
Set Speed Dials
You can touch and hold the 1 ~ 9 keys from the dialer to call the
corresponding speed dial number.
The number key 1 is reserved to speed dial your voicemail.
To assign a speed dial key:
1. Touch the Home key >
Settings > Call settings > Speed dial.
> (in the top search field) >
> (in the top search field) >
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