What does Mobile mean when it says that the other party has opened a short message service?

I received this prompt because the other party's mobile phone was turned off without power, turned on flight mode, or there was no signal.

The other party's mobile phone number has opened a mobile data service called "Call Reminder".

Incoming call reminder means that when the mobile phone is turned off or out of service area, it will save the incoming call information for the other party within 24 hours through the incoming call reminder platform. After the mobile phone returns to normal, all incoming calls will be sent to the other party's mobile phone in the form of short messages, so that important incoming calls will not be lost.