How can I decline a call in iPhone when the screen was locked? I have an iPhone 4S. I really don't know in which basis it shows Answer/Decline buttons when someone calling me. Sometimes it shows both buttons and sometimes it only show the option "Slide to answer".



The scenarios are,


The iPhone is locked/unlocked
The iPhone is in normal mode/silent mode


Note: I does not use Voice mail. I just need the "Decline" button in any mode/ any situation, because the mobile mode should not decide to hide the decline button. The owner of the mobile should decide it!
Push the power button on the top of the phone twice. The first time, the call is silenced. The 2nd time the call is rejected/directed to voice mail (if set up).