Tip: How to Quickly Silence a Ringing iPhone
Below are a few tips from iPhone Alley on how to quickly silence your iPhone when receiving an incoming call. They also show you how to send those calls to voice mail.
press sleep/wake (top) button to silence iPhone
or press volume button (either one) to silence iPhone
quickly press sleep/wake button twice to send incoming call to voice mail
quickly press button on iPhone headset twice to send incoming call to voice mail