A withheld number is a number that has been blocked from being released. The message ‘withheld’ is returned if the person being called uses 1471 to find out the identity of the caller.
The withhold number service is controlled by a caller on a per-call basis using the prefix ‘141’ or on every call if the Permanent Number Withholding facility has been subscribed to. Switchboards may also withhold their numbers on outgoing calls. This affects all extensions so a customer with ACR being called by anyone with one of those extensions will reject the call.