Apple iPhones have a distinct "Silence Unknown Callers" feature, which sends calls from numbers not in your contacts straight to voicemail.
However, situations arise where a user needs to receive an important call from a private number—such as a doctor’s office, a job offer, or a government agency—or wishes to identify who is calling. This paper explores the mechanisms behind private numbers, the technical steps to unblock them, and the legal methods available to identify anonymous callers. unblock a private number