During an active call, the Mute feature prevents the party (with whom you are speaking) from hearing you. This feature is most commonly used in conjunction with the Speaker phone. However, it can be used to hold an off-line conversation at any time during a call.
To prevent the other person on the line from hearing you:
1.Press 
MUTE. The indicator next to the Mute button lights when Mute is active.
2.To reinstate two-way conversation, press MUTE again.