Coding problem: How to automatically send short messages to the mobile phone number left by the user at an accurate appointment time through the computer?

This is very difficult. Generally, companies with this business have cooperation with communication companies, and the server will send requests to the communication companies when necessary. But it is difficult for ordinary people. And all I can imagine is to realize this problem through Fetion. But you have to be able to use the program to operate the computer Fetion. After the user registers, your server will automatically operate Fetion to send a Fetion request to this mobile phone after receiving the user information. Then the program sends information by fetion when there is a time monitor (based on the current time) and other systems as the reserved time. I can only think of this way. After all, ordinary people have no business dealings with China Mobile Unicom.