DID stands for – Direct Inward Dialing (also called DDI in Europe) and is a feature offered by telephone companies for use with their customers’ PABX system, whereby the telephone company (telco) allocates a range of telephone numbers associated with one or more phone lines. DID allows a company to assign a personal number to each employee, without requiring a separate physical phone line for each to connect it to the PABX. That way, telephony traffic can be split up and managed more easily.
DID requires that you purchase an ISDN or Digital line and ask the telephone company to assign a range of numbers. You will then need DID capable equipment at your premises which consists of BRI, E1 or T1 cards or Gateways.