A telephone number that routes directly to a specific user, device, or service on a customer's phone system, commonly sold by VoIP providers in large quantities.
DIDs originally let callers reach an individual extension behind a PBX without going through an operator or attendant. In VoIP, the term is used more broadly for any telephone number a provider assigns to a customer and routes to their trunk or application. They can be local numbers, toll-free numbers, or international numbers, depending on what the provider offers.
Providers obtain DIDs from their own numbering resources or from upstream carriers and assign them to customers. The provider's records of which customer holds which number are the basis for deciding whether calls presenting that number qualify for full attestation. When a customer ports numbers away, or a number is disconnected, those records must be updated promptly so the signing service does not keep vouching for numbers the customer no longer holds.
DIDs are also a resource that bad actors seek out. Large orders for numbers across many area codes, especially from new accounts, can indicate a plan to rotate calling numbers in a snowshoe robocalling campaign or to present local-looking numbers to targets. Reviewing number orders against the use case the customer described during onboarding is a simple, low-cost check.
Why it matters to carriers
Your DID inventory is both a revenue line and a compliance record. Accurate assignment data supports correct attestation and fast traceback answers, while monitoring how customers order and use numbers can reveal abusive campaigns before they generate complaints or regulatory attention.