How often are you sitting in a meeting, or a movie, or in church, when someone’s iPhone starts ringing (often with some creative and very distracting sound)? This is often followed by the sound of someone clawing through their bag or pocket, trying to find the offending device to silence it.
Of course, the best solution is to have remembered to set the “silent switch” beforehand. But even at this tell-tale moment, there is a simple, hopefully quick, solution. Just reach into your pocket or bag and squeeze the iPhone to hit either volume button on the side of the iPhone. This will instantly stop the ringer from sounding an alert or vibration, without hanging up. Thus the caller thinks it is still ringing.
Remember, it is just one hit of either button, and this call is silenced — it does not affect future calls.
If you’d like to know more about the details, see this article in OSXDaily.