Anonymous Call Rejection on the iPhoneby Lara Webster
Most incoming calls on the iPhone show you exactly who is on the other end of the line. In some cases, however, a call may have disabled your ability to see the number from the other end of the call. Rejecting an anonymous caller takes just a few seconds, but you cannot stop someone from leaving messages on your phone's voicemail.
Every iPhone has a caller ID function. When you receive an incoming call, the phone number of the caller is displayed on the front of the phone; sometimes, the city and state of the caller is also shown. If you have saved a particular phone number to a contact, the contact's name appears when she calls you. When someone has disabled the outgoing caller ID on her cellphone or landline, you will see a "Blocked" or "Unknown" message when she calls your iPhone.
Locked iPhone Call Rejection
When your iPhone is in lock mode and you receive a phone call, a "Slide to Answer" message appears on the screen. If the caller is anonymous and you don't want to take the call, you can reject the call by pressing the "Sleep/Wake" button twice in a row. The call is immediately sent to your iPhone's voicemail.
Unlocked iPhone Call Rejection
When your iPhone is unlocked and you are using an application on the device, your activities are interrupted by the caller ID along with "Accept" and "Decline" buttons. Likewise, if you are currently on the phone the buttons appear. If you receive an anonymous call, tapping the "Decline" button once will send the caller straight to your voicemail.
You cannot set your iPhone to automatically reject all anonymous calls. Each incoming call, regardless of whether or not the phone number is visible, must be either accepted or declined manually. Users cannot force a phone number to be revealed on their phones if the caller has hidden her number.