What is a call reminder message?

Are you asking what a call reminder is? The meaning of this function is as follows:

Incoming call reminder means that when the mobile phone is turned off or out of service area, the incoming call information within 24 hours is saved through the incoming call reminder platform. After the mobile phone returns to normal, all incoming call information is sent to the mobile phone in the form of SMS.

After the call reminder is turned on, when the mobile phone is turned off or out of service, a friend calls and hears the prompt "Hello, the subscriber you dialed has turned on the call reminder function. We will inform the other party of your call information by SMS. Thank you for calling. Please hang up and see you later. " There is no charge for this call.