DID (direct inward dialing)

Before DIDs, a company with one main number needed a receptionist to transfer every call. Direct inward dialing let carriers pass the dialed digits to the company's PBX, so each employee or department could have its own reachable number without a separate physical line.

Today most DIDs are delivered over IP:

1. A caller dials the DID.
2. The carrier routes the call to the customer's SIP trunk or cloud phone platform.
3. The PBX reads the dialed number and sends the call to the configured destination: a desk phone, softphone, IVR menu, call queue or forwarding rule.

DIDs are usually drawn from geographic landline ranges or, in some countries, non-geographic ranges. Many can also be enabled for SMS, depending on the provider.

A DID lives in a phone system rather than on a mobile network subscription. That makes DIDs excellent for business calling: cheap to add in bulk, easy to reroute, and portable between PBX providers.

The trade-off shows up in verification. A carrier lookup typically reports a DID as landline or VoIP, and services that restrict sign-ups to mobile lines may refuse it. Some DIDs also cannot receive SMS at all. A real mobile number is reported as mobile, which is why people who mainly need to receive codes often choose one instead. See non-VoIP vs VoIP numbers.

• A support team gives each regional office its own local DID, all routed into one cloud contact center.
• A small agency assigns a DID per client so incoming calls ring the right account manager.
• A developer maps a DID to an app that answers calls with an IVR.

In each case the number exists to route inbound calls inside a phone system, which is also why DIDs are often counted among what people call virtual numbers.