When I call someone, his cell phone is turned off, and when he turns it on, my cell phone will receive SMS notification. What kind of business is this?

Hello, the "incoming call reminder" service refers to the missed message reminder service for incoming call users. When the called user is busy, turned off or unable to connect (there is no signal when busy), the caller accesses the missed call service system, and informs the called party of the incoming call information when the called party can arrive according to the calling identity and the calling party's choice, thus ensuring that the calling party and the called party's incoming call information are not lost and giving the user a better experience. You can go to the online business hall or the communication 100 business hall to handle this business.