What's wrong with hands-free SMS? What's the difference between it and ordinary SMS?

A control character is added to the head of the short message. As long as it is received by the hands-free mobile phone, it will be displayed in hands-free form. The sending process and cost are exactly the same as ordinary SMS.

But on the website, the website takes hands-free as a selling point and deliberately raises the price to make huge profits.

In addition, some old mobile phones do not support such short messages, which can easily become garbled.