A service provided by a local exchange carrier (LEC) to a corporate client. Direct inward dialing (DID) uses a Private Branch Exchange (PBX) that allows outside callers to directly dial individuals within the company.
The LEC allocates a block of phone numbers to the company, usually differing only in the last two, three, or four digits. For example, a company with 50 employees who each need a separate phone number could be assigned the numbers 555-1201 through 555-1250. Outside callers could dial the employees directly using these numbers, which are routed through perhaps only eight trunk lines that service the PBX, supporting a maximum of eight simultaneous calls. Inbound calls are routed by the PBX to the appropriate extension.