The Primary Extension is an optional feature in Provisioning Solutions, it is the main extension of a Phone Number Range. Primary Extensions will be marked and will never be assigned automatically by the system but may be assigned manually, however the Primary Extension cannot be changed.
It is typically the extension that a carrier will present to a called party if the calling party identifier is missing, suppressed or invalid. Frequently, enterprises use the Primary Extension as the main phone number they provide to customer and is advertised in their company literature. The Primary Extension is often the first extension of a range, however the Primary Extension does not have to be part of the extension range.