A DID number (Direct Inward Dialling) is a virtual phone number that routes incoming calls to a specific destination โ typically an extension, department, or device โ without requiring a dedicated physical phone line. DID numbers are provisioned via a telephone carrier and delivered over VoIP or SIP infrastructure. Businesses use DID numbers to establish local presence in multiple countries, provision numbers by the thousands via API, and assign unique inbound numbers to agents, teams, or services. Also referred to as DDI (Direct Dial-In) in Europe.
A DID (Direct Inward Dialling) number is a virtual telephone number assigned by a carrier that routes inbound calls to a configured destination โ a SIP address, PBX extension, softphone, or any phone number. When someone dials your DID number, the carrier receives the call and forwards it over SIP or via a carrier trunk to wherever youโve pointed it. There is no physical line associated with the number; routing is entirely controlled through the carrierโs portal or API, making it easy to redirect or reassign numbers instantly.
A traditional phone number is tied to a physical line or circuit installed at a fixed location. A DID number is a virtual number with no physical infrastructure โ it exists in software and is routed over the internet. This means a DID number can be based in one country and ring a phone in another, can be reassigned instantly, and can be provisioned in bulk via API. For businesses, this makes DID numbers significantly more flexible and cost-effective than traditional PSTN line-based numbers.
Coverage varies by provider. IDT Express offers DID numbers in over 140 countries, covering most major markets in North America, Europe, Asia-Pacific, and Latin America. Some countries have regulatory restrictions on virtual number provisioning โ for example, requiring local business registration or address verification before issuing numbers. Coverage for geographic (local) numbers, national numbers, and toll-free numbers also differs by country. IDT Expressโs DID number coverage map shows available countries and number types.
IDT Express provides a REST API for programmatic DID number provisioning. You can search available numbers by country, area code, or number type; purchase numbers; configure routing (forwarding destination, failover, caller ID); and manage your number inventory โ all via API calls. Authentication uses API key-based access. Full API documentation including endpoint references, request/response examples, and SDKs is available in the IDT Express developer portal.
