Apple's mobile phone calls have sound, and SMS messages have no sound. What happened?

Because the voice of SMS is independent, after mute is set, there is no sound when SMS comes in.

First, in the main menu interface, click Settings.

The second point to note

3. Click the message, click "Allow notification", click "Notification sound", and select the "Reminder ringtone" of the short message. The top one is "None", which means that no sound is made when sending short messages, and everything else is audible.