How do users open the service of missing letter reminder?

Missed call reminder service is a voice value-added service based on call forwarding, which is aimed at called users. The called user can freely set up the missed call reminder service platform before the call, for example, the user can switch to the missed call reminder service before the call is busy and there is no answer, or set up the missed call reminder service unconditionally.

Opening mode of missed message reminder service:

Charging rules: