How to send short messages to mobile users with Tietong's landline?

How does the landline send short messages to mobile users? Actually, it was sent by the mobile phone number.

Such as mobile wireless land lines. Push a 7-digit fixed number to the user. In fact, fixed numbers and mobile phone numbers are bound in one-to-one correspondence. Fixed number is just a way of displaying, in fact, mobile number is used for interactive transmission of information.

So, the principle of sending text messages by landline is like this.