0 used to refer to a phone number that is not made public by the phone company:
1 used for describing a telephone number that is not in the public telephone directory (= book that lists numbers) and is not given by the telephone company to people who ask for it:
A disadvantage is that the list does not contain households with ex-directory telephone numbers.
Addresses of potential controls where a telephone number was unavailable (because the household was ex-directory) were discarded.
It is important to note that being an ex-directory customer does not guarantee that unsolicited calls will never be received.
An example here is that unless my telephone number is ex-directory, anyone can get my telephone number and address.
The present number is ex-directory and only after a considerable amount of research and pressure was it possible to make contact.
Is not the cure for that the provision of a number of ex-directory lines to which the clerks of councils have access?
They can act as collecting centres for information about local supplies and conditions and can quickly phone the ex-directory numbers.
Police had to be posted and the victim's telephone made indefinitely ex-directory.
