Why your iPhone can 'accept' or 'decline' some calls but only 'slide to answer' others

Even with access to a plethora of information at their fingertips, iPhone users are plagued by not knowing why their phone calls come in two different ways: swipe to accept, or press to decline.

On Friday, Twitter personality Freddy Cabrales posted a tweet illustrating his frustration at not knowing why calls come in two different ways.

Cabrales' tweet went viral, which prompted Business Insider to initiate their own investigation into the calling conundrum. Here is what they found out below.

Does the slide to accept screen appear when your iPhone is receiving a call from someone not in your contacts? Result: No.

Does the slide to accept screen appear when your iPhone is receiving a call from a number not associated with an Apple device? Result: No.

Does the slide to accept screen appear when your iPhone is receiving a call while it is in lock? Result: Yes!

There it is, the only reason the slide to accept screen appears instead of the accept/deny is because your phone is in lock.