There are a number of reasons why an incoming call may be displayed as “unknown.” These include situations where the number is unlisted or made through a VoIP service or app. When a number is unlisted, it means the person, company or organization is trying to keep their information private by intentionally removing it from directories like Whitepages and Yellow Pages. With VoIP services, callers can request phone numbers through services like Google Voice which can display as “unknown caller” if there is no profile name on the digital voice account. Reverse phone searches can still be used to track down information about these numbers.