The ANAC facility is useful primarily during the installation of landline telephones to quickly identify one of multiple wire pairs in a bundle or at a termination point.
No official lists of ANAC numbers are published, as telephone companies guard against abuse that would interfere with availability for installers.
[1] The North American Numbering Plan reserves the exchange (central office) prefixes 958 and 959 for plant testing purposes.
ANAC services are typically installed in the 958 range, which is intended for communications between central offices.
[citation needed] Some telecommunication carriers maintain toll-free numbers for ANAC facilities.