Direct Inward Dialing (DID) is used interchangeably with “telephone number” in Peeredge SBC documentation. DID is a service provided by a carrier (e.g. 46 Labs) that allows a phone call to ring to a direct line rather than having to pass through a phone tree or menu in order to be routed to its end location.
The term originates from a time when it was more common for offices to avoid individual phone numbers for employees and instead utilize extensions. The DID service also provides DNIS. VoIP carriers typically deliver DID calls to their customers in an E.164 format.