What does SMS call service mean? How to explain SMS calling service?

1, you don't need to set the number, and you can't get through with other mobile phones.

2. SMS call means that when you turn off your phone or are out of service area, all your incoming information will be automatically recorded, and when you turn on your phone, these information will be sent to your mobile phone in the form of SMS.

3. Your classmate's cell phone is turned off or out of service. When he is turned on or has a signal, he will receive the message that you call him. You don't need to set a number, just open this service in the business hall.