What does it mean for Unicom number to enable the missed message reminder service?

Unicom missed call reminder service means that when a caller calls the owner and the owner can't answer the phone (that is, it is out of service area or turned off), the system will automatically broadcast to the caller: "Hello, the subscriber you dialed has used the manual secretary service", and the system will automatically notify the owner of the call information by SMS after the caller hangs up.