Caller ID is a telephone service that transmits the phone number of the calling party to the receiving party of the call, the phone number of the caller being their "Caller ID". Sending the unique number allows the receiving party to know who the incoming caller is so the call can be handled appropriately and missed calls can be returned.
Generally a callers phone will transmit their Caller ID by default, but this configuration can be changed in several ways to instead show "blocked" or "unidentifiable" to the receiving party:
- Within the settings of the phone (eg for iOS: Settings > Phone > Show My Caller ID)
- By dialling a specific code before the number (eg 1831 or #31# for Australia, varies for other countries)
- By requesting Caller ID to be disabled through the calling phone provider.
The receiving party also needs to have the capability to receive and display the Caller ID. This is generally always available for mobile phones, but landlines may need to enable this service with their phone provider and purchase additional hardware.
More information on Caller ID can be found here: https://en.wikipedia.org/wiki/Caller_ID