Why does the number called by the school motto caller be different every time?

Virtual number. It is used by teachers to log in to the school communication platform to send text messages. The virtual number is the number displayed on the mobile phone when the teacher sends text messages on the platform. A virtual phone (also known as one number) is a never-busy, removable local phone number that integrates multiple functions such as calls, faxes, messages, emails, text messages, call transfer, automatic paging, password protection, etc. It is more powerful and complete than traditional call transfer and is a telecommunications service.