The exchange line authorisation determines which phone number types can be dialled by a subscriber (e.g., phone numbers in the local phone network).

Call deblockers can be added to the exchange line authorisations to expand dialling options with additions of a certain supply of numbers (phone numbers for specific connections or specific prefixes, released numbers). Since call deblockers have a higher priority than call restrictors, they can be used to release restricted numbers or parts of them.

In order to restrict exchange line authorisation, the phone numbers that should not to be dialled can be put in call restrictors (restricted numbers). There are several ways to do this. In general, phone numbers are restricted that begin with a certain digit sequence and that should not be accessible to every subscriber due to its higher charge tariffs, e.g., 0900 phone numbers. Normally, the first 4 to 5 digits indicate the phone service that cause such high charges.

If an attempt is made to dial a restricted phone number, only a busy signal is heard. If the restricted numbers are not enabled (meaning "not restricted"), restriction via the configured exchange line authorisation is still possible.