What is a DID number?

A DID number (direct inward dialling) is a phone number that rings straight through to one person, team or menu on a phone system, with no operator in between. In the UK and much of Europe the same thing is called a DDI, direct dial-in.

Seen from the buyer's side, a DID is a virtual phone number: it has no line of its own, and the phone system decides where it rings (more on what a virtual phone number is). Many DIDs share one connection to the phone network, today usually a SIP trunk; if that is new, start with what a SIP trunk is.

Updated 10 November 2026.

1:N

Why DID numbers matter

Give everyone a number without giving everyone a line.

Before DIDs, every public number needed its own physical line, or callers went through a switchboard. With DIDs, one trunk carries calls for every number, and you size the trunk by how many people talk at once, not by how many numbers you publish.

How a DID number works

The dialled number travels with the call. The phone system reads it.

Every incoming call on the trunk says which number the caller dialled. An inbound rule in the phone system matches it and rings the destination you set for it.

+44 20 7946 0101QSales queue
+44 20 7946 0102210Accounts, extension 210
+44 20 7946 0103IVRSupport menu

Three DIDs on one trunk, each ringing somewhere different. Example numbers from Ofcom's range kept for drama.

DID vs extension vs main number

Three numbers a phone system uses, and what each one is for.

DID

DID number

A full public number. Anyone can dial it from any phone, and it rings one chosen destination with nobody transferring the call.

210

Extension

A short internal number such as 210. It works only inside your phone system, for colleagues calling each other.

Main number

One public number for the whole company. A receptionist or a menu answers and passes the caller on.

DIDs and extensions often work together: the DID +44 20 7946 0102 can ring extension 210, so a customer reaches Accounts directly while colleagues still dial 210.

PBX

Where to set up a DID

Each phone system calls the matching rule something different.

The trunk itself must already work (SIP trunk configuration). A SIP app on one phone needs no rule at all; every DID on its login rings it.

3CX
Each DID is assigned to a user, a queue or a menu. A number with no assignment falls to the default rule.
FPBX
FreePBX: one inbound route per number, with the number typed into its DID field and a destination chosen below.
*
Asterisk: an exten line for the number, in the dialplan context your trunk delivers calls into.
YST
Yeastar: an inbound route on the trunk, with a DID pattern that matches the number and the destination it rings.

FAQ

DID number questions

Is a DID number the same as a virtual number?

In practice, yes. Virtual number is the name for what the buyer gets; DID is the name for how a phone system receives it.

What does DDI mean?

Direct dial-in, the British and European name for a DID. A UK provider selling DDIs is selling the same thing as a US provider selling DIDs.

Can one DID ring several phones?

Yes. Point its inbound rule at a ring group or a queue instead of a single extension, and every phone in it rings.

Do I need a SIP trunk to use a DID?

You need something signed in to the SIP login the DID is delivered to: a phone system with a trunk, or a SIP app on a single phone or computer.

What is a DID block?

A range of consecutive numbers issued to one company, so the last digits can match its extensions. Carriers sold DIDs this way long before SIP; today most are ordered one at a time.

How much does a DID number cost?

Usually a monthly fee per number; some providers add a setup fee and a price per incoming minute. LinkedSIP charges $0.99 a month per number, with incoming calls free.

One trunk, as many DIDs as you need. Each rings where you say.

Order a DID number Back to virtual numbers