Direct Inward Dialing (DID), also known as DDI in Europe, is a telecom service that allows businesses to assign individual phone numbers to employees without needing separate physical lines. DID is a feature that allows a company to assign a personal number to each employee, without requiring a separate physical phone line for each employee to connect to the PBX. By setting up these virtual numbers, inbound calls can be routed directly to the desired extension. This way, telephony traffic can be split up and managed more easily.

In contrast to Direct Inward Dialing, Direct Outward Dialing (DOD) is a local exchange carrier service that allows team members within the PBX system to make outbound calls directly. DOD bypasses having to press a number before connecting to the operator, or dial other numbers first.

Caller: A customer or client dials your business’s assigned DID number. This unique number is linked directly to a specific extension or department, ensuring their call reaches the right person without the need for manual routing or going through an Interactive Voice Response (IVR).

SIP Trunk: The call is then transmitted via a SIP Trunk, a virtual phone line that connects your business to the public telephone network.

Internet: The SIP Trunk sends the call through the internet instead of traditional copper phone lines, making the process faster and more flexible. This digital route ensures seamless call quality and allows for scalable, cloud-based communications.

PBX: Your PBX (Private Branch Exchange) receives the call and intelligently routes it to the appropriate extension based on the assigned DID. This automated system ensures efficiency, keeping your communications streamlined and professional.

PBX Users: The designated PBX user receives the call directly on their phone or softphone. Whether it’s for customer support, sales, or management, the caller is instantly connected to the right person, improving customer satisfaction and internal productivity. This is the core benefit of Direct Inward Dialing—fast, targeted call delivery without human intervention or shared extensions.

If an organization has 25 employees and each employee has a separate telephone number, or extension, within its physical location, the organization can rent 10 physical trunk lines from the telephone company. This will allow 10 phone calls to take place simultaneously.. Anyone dialing into the system while all 10 lines are in use would get either a busy signal or be directed to a voice mail system. A DID number can also be used for fax and voice transmissions.

To set up Direct Inward Dialing, you’ll need a SIP or ISDN trunk and a PBX that supports DID. Your provider will assign a block of phone numbers, which you can map to extensions or devices using your PBX system.

The benefits of having a direct phone number for each employee apply to every sized business today. 

These include: