How does Apple's mobile phone 12 automatically send short messages to China Mobile when it is turned off?

Apple mobile phone 12 is turned off and turned on automatically. The steps of sending SMS to China Mobile are as follows:

1. On the Apple Settings page, enter the Information Application Settings page.

2. On the information application settings page, turn off the iMessage information function.

3. Turn off the filtered receipt of the sent information to prevent the Apple mobile phone from automatically sending short messages for no reason.