[Update: This tip continues to work in iOS 10.]
You likely have noticed an irritating (to some of us…) difference when receiving a call on your iPhone when the screen is locked vs. when it’s unlocked.
When it’s unlocked and someone is calling you, you will see two circular icons: a green one that accepts the call and red one that declines call. However, when your screen is locked, you will only see a “slide to answer” gesture option for answering the call along with “Remind Me” and “Message” options. There is no decline call option on your screen when it is locked.
There are, however, still ways to reject the call without the “decline” icon present and put an end to the incessant ringing. To do this, you can simply double tap the power button at the top (iPhone 5S/C or earlier) or side (iPhone 6 or 6 Plus) of your iPhone. And a single tap of the power button – or volume button – will silence the received call without ending it.
If you want a decline the call, but also make a note of the call so you don’t forget about it completely, simply select “Remind Me” and you’ll be prompted to enter the time you would like to return the call. Another decline option is to press “Message” and you’ll be able to send a text message to the caller.
And if you continue to get calls from an unwanted or unrecognized number, you can always block the caller via this tip from the Rocket Yard.