When a call comes in, you may not want to answer it, or you may need to stop iPhone from ringing or vibrating. You can silence or decline an incoming call.
When you silence a call, you still have a chance to answer it, until the call goes to voicemail. When you decline a call, the call is silenced and sent directly to voicemail.
Silence a call
Press the Sleep/Wake button once, or either of the volume buttons.
Decline a call
Do one of the following:
Press the Sleep/Wake button twice quickly.
Press and hold the mic button on the headset for about two seconds, then let go. When you let go, two low beeps confirm that the call was declined.
Tap Decline. Decline appears only when you’re using iPhone.