When receiving an incoming call, you can quickly press the power button (that is the button on the top of your device) once to mute the ringing. Or, when receiving an incoming call, you can quickly press the power button twice and send the call straight to voicemail!
This would be my one pet peeve about this iPhone 4s. I cannot find an answer as to how to change the number of rings or the length of the ringtone anywhere. This should be a basic option of any cell phone, in my opinion. My phone rang today during an inconvenient time and I cringed until it stopped. Is there even an option to "ignore call"? I loved that the Evo could set the number of rings or I could ignore the call or take the call. I don't have that option with the iPhone and I don't like that. Any suggestions?