What is a DID (Direct Inward Dialing) number?

A DID (Direct Inward Dialing) number is a public phone number that routes an external caller directly to a specific destination (a person, queue, IVR, or application) without passing through an operator or main switchboard. DIDs let organizations assign individual reachable numbers without a dedicated physical line for each.

How it works

A provider allocates one or more phone numbers from its inventory (or the customer brings numbers via a carrier). Each DID is mapped to a routing target so that when the number is dialed on the public network, the platform delivers the call to the configured destination. Numbers can be local, national, toll-free, or international, and a single trunk can carry calls for many DIDs at once. On SIP.IO, DIDs are provisioned and routed alongside numbers and extensions.

Why it matters

DIDs make it possible to publish distinct numbers per department, campaign, region, or individual, while sharing capacity over SIP trunks. This supports direct reachability, local presence in multiple regions, and granular routing and analytics, all without one-line-per-number hardware.

FAQ

What is a DID (Direct Inward Dialing) number? A DID is a public phone number that routes an external caller directly to a specific internal destination (a person, queue, IVR, or application) without an operator or main switchboard.

What is the difference between a DID and an extension? A DID is a full external number anyone on the public network can dial; an extension is a short internal number within a phone system. A DID can be mapped to an extension so outside callers reach an internal destination directly.

Related: What is SIP trunking? · What is an IVR? · Numbers & Extensions