Will you know if you call the user and text him to inform him that he is busy?

Call the user's busy tone to inform him that he will know.

Even if the other person can't answer the phone at that time, you can check the message at your convenience and know that you have contacted yourself. The purpose of the call reminder service is to ensure that you will not miss important calls because the other party is busy. When the other party receives such a short message notice, they will know that someone has contacted, and they can choose a suitable time to call back.