But you can guess any whole number if you have an unlimited amount of tries. if you are interacting programmatically with a live system there is always a limit to the number of tries that you can do.
iPhones and most other devices are limited. After a few tries, you will start down an increasing lock-out time for the next guesses. The back out does not apply to changing the PIN of an unlocked phone to see if that PIN gives a warning.
TL;DR: You can find the blacklist this way but not unlock a phone.
