HTC One M8 for Windows - Manual (Page 106)

Muting the microphone during a call
On the call screen, tap mute.
To turn the microphone back on, tap mute again.
Starting a three-way call
Three-way conference calling with your friends, family, or co-workers is
easy. Make the first call (or accept a call), and then dial another contact to
add it to the conference.
1. Make a call to the first conference call participant.
2. When connected, tap add call, and then call the second participant.
The first participant is then put on hold.
3. When connected to the second participant, tap merge calls.
4. During the conference call, you can:
§ Tap flash to hang up on the second participant and talk to the
first person dialed.
§ Tap end call to end the conference call.
106 Phone calls