DID (Direct Inward Dialing)
A DID is an externally-dialable phone number that routes inbound calls directly to a specific endpoint (extension, IVR, queue, AI agent) on a PBX or SIP trunk — without going through a switchboard operator. The term originated in 1960s analog telecom; today it just means 'a real phone number you can rent and route however you want'.
Modern usage
In SIP/cloud telecom, 'DID' is synonymous with 'phone number'. A DID has:
- An E.164 number (the externally dialable address).
- A routing target (your SIP trunk, a forwarded PSTN number, an IVR, etc.).
- Optional features: SMS, fax (T.38), CNAM registration.
Geographic vs Toll-Free vs Mobile
| Type | Examples | Caller pays | Use case |
|---|---|---|---|
| Geographic | +1 415, +44 20, +49 30 | Yes (local rate) | Local presence |
| Toll-free | +1 800, +44 800, +49 800 | No (callee pays) | Inbound customer service |
| Mobile | +44 7XXX, +49 15X-17X | Mobile rate | SMS, 2FA, mobile-style branding |
| National non-geo | +44 03XX, +49 0180 | Geographic rate | National brand presence |
Related terms
Related glossary terms
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BYOC is a deployment model where you use a third-party SaaS platform (Vapi, Retell, Microsoft Teams, Zoom Phone, Twilio Flex) for the call-c
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