I just learned today from the iPhone iOS 7 manual that it depends if your phone is asleep or active.
If it is active, then you are given the choice of Accepting, Declining, or something else.
If it is asleep (inactive) then you are only given the choice of swiping to accept the call. But if you have read the manual, then you know that you must quickly press the "sleep" button twice to decline the call.
The unsolicited callers have set their robots to go through a long list of cell phone numbers. Sometimes a specific number is given, and you can find on Google that the number is an outgoing call center. Sometimes the screen shows something like unidentified caller.
It is a real nuisance to be outside on a bright day with gloves on with the phone buried in an inside pocket when one of these callers attacks. Get the phone out! Try to see who the call is from. Take off a glove to click the sleep switch twice.
Yep! The Macintosh WAS the computer for the rest of us!