Press-to-talk (PTT) (Zenitel Connect Pro)
From Zenitel Wiki
Normal two-way calls are by default in open duplex with echo cancelling.
Zenitel native devices support press-to-talk options to override open duplex:
Press M key: Enter Talk mode, speaker muted. On the M-press device send a DTMF '*'
Release M key: Return to open duplex. On the M-release device send a DTMF '#'
ZCP relay the DTMF '*' / '#' events to the remote device.
Speech mode of Zenitel native devices is also controlled by DTMF '*' / '#' events received from remote:
On receive DTMF '*' : Enter Listen mode, mute microphone
On receive DTMF '#' : Return to open duplex
This require no configuration. But does not apply if neither of the devices in the call are Zenitel native device.