DID
A DID (direct inward dialing number) is a phone number that routes straight to a specific destination, such as a person, a department or an automated receptionist, without passing through a switchboard.
Also called: direct inward dialing, dedicated phone number, virtual number
Businesses buy DIDs in blocks or one at a time from a carrier or a hosted phone provider. Each one is a real, dialable number that can be pointed at whatever should answer it. For a hosted receptionist, the DID is the number the service answers on. The business either publishes it directly or forwards its existing number to it.
Forwarding is the reversible option. The published number stays with the current carrier, and a forwarding rule (always, on busy, on no answer) sends calls to the DID. Porting moves the published number itself to the new provider, which is permanent in practice and takes days to complete. Forward first; port once the receptionist has proved itself.
A DID is also the number a receptionist shows when it calls or texts out, so it is worth registering the caller ID that customers already recognize.