Numbering

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