AT&T 7406BIS - Manual (Page 52)

To mute the 1 Press [
Mute
]
microphone associated
Red light goes on and other party cannot hear you
with the handset so the
●
other party cannot hear 2 Press [ Mute ] again to resume talking to other party
you through handset
●
Red light goes off and other party can hear you again
To change from 1 Lift handset and talk
speaker to handset
To change from 1 Hang up handset
handset to speaker
2 Press [ Speaker ]