A DID phone number (Direct Inward Dialing) is a real telephone number that a provider routes to your phone system over the internet, so outside callers reach a specific person, team or application directly. In VoIP, a DID number is the inbound side of a SIP trunk: the trunk carries the calls, the DIDs are the numbers people dial to reach you.
What does DID number mean?
DID stands for Direct Inward Dialing (in Europe the older term is DDI, Direct Dial-In). The idea comes from traditional PBXs: a company had a block of numbers on its lines, and the PBX used the last digits to ring the right extension without an operator. In VoIP, a DID is simply a number from the national numbering plan that a provider points to your SIP trunk, PBX or platform. When someone calls it, the provider sends an INVITE to you with the dialled number, and your system decides where the call goes.
What types of DID numbers exist?
| Type | Example use | Notes |
|---|---|---|
| Geographic (local) | Office number in a city | Some countries require a local address or proof of presence |
| National (non-geographic) | Single number for a whole country | Format and caller cost depend on the country |
| Mobile | Numbers that can also receive SMS | Not available as VoIP numbers in every country |
| Toll-free | Customer service lines paid by the receiver | National numbers per country (see ITFS vs UIFN) |
Many countries ask for identity and address documents before activating numbers, and some restrict who can hold them. This is the same reason providers run KYC checks.
What is the difference between a DID and a SIP trunk?
A SIP trunk is the connection; a DID is a number delivered over it. One trunk can carry hundreds of DIDs, and the number of simultaneous inbound calls is limited by the trunk's channels, not by the number of DIDs. You can also have DIDs without your own trunk, for example numbers on a hosted PBX, or trunks without DIDs, for example a route used only for outbound calls. See what is SIP trunking for the connection side.
VoIP vs DID: are they the same?
No. VoIP is the technology; a DID is a phone number. A DID becomes a "VoIP number" when the provider routes it to an IP destination. In wholesale, the two directions have their own names: calls to your DIDs are origination, and calls you send out are termination (see origination vs termination).
How do DID numbers work with your phone system?
- You order numbers in the countries and cities you need.
- The provider points them to your SIP endpoint (IP address or registration).
- Calls arrive with the DID in the request URI or the To header, usually in E.164 format.
- Your PBX matches the number to an extension, queue, IVR or application.
Contact centers often use DIDs as the caller ID on outbound calls, so customers see a number they can call back. Present only numbers you hold, and keep them answered: unanswered or unreturnable numbers get labelled as spam faster. Rules on caller ID are covered in CLI spoofing rules.
What should you check with a DID number provider?
- Coverage: countries, cities and number types available, and stock in each.
- Requirements: documents and local address rules per country, and activation time.
- Pricing: setup fee, monthly fee per number and any per-minute inbound charge (common on toll-free).
- Channels: how many simultaneous inbound calls are included.
- SMS: whether the number can receive text messages, if you need it.
- Porting: whether you can port existing numbers in and out.
Numbers and routes together
Most businesses with DIDs also need outbound routes. VoIPMatcher sources VoIP termination routes from its carriers and manages them for you; your data is never shared or sold. Request a VoIP route and tell us the destinations you call.
Frequently asked questions
What is the full form of DID number?
DID stands for Direct Inward Dialing. It describes a telephone number that rings a specific extension, group or application directly, without passing through an operator or a main switchboard number. In Europe the same service is often called DDI, Direct Dial-In. In VoIP, DID usually means any number routed to a SIP trunk or PBX.
Can a DID number receive SMS?
Some can. It depends on the country and the number type. Mobile numbers and many US and Canadian local numbers can be SMS-enabled, while most landline and toll-free numbers in other countries cannot receive texts. Ask the provider for SMS support per country before you order, as voice and SMS are often separate services.
Can I make outbound calls with a DID number?
A DID itself only receives calls. Outbound calls go through a SIP trunk or termination route, and you can usually set the DID as the caller ID so people see a number they can call back. Make sure the outbound route passes that caller ID correctly and that you have the right to present the number.
How many calls can one DID number receive at once?
A DID has no fixed limit by itself. The number of simultaneous calls depends on the channels of the trunk or account it is routed to, and on what your PBX can handle. If your trunk has 10 channels, one DID can receive up to 10 calls at once, shared with any other DIDs on that trunk.
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