Is it accurate to change SMS to mobile phone password? How much is a short message?

Dear, if you change the password of mobile phone service by sending a letter instruction related to password change to 100 10, and the change is successful, then the instruction you sent is accurate. Please take good care of your mobile phone service password after the change. You can use this password to handle various businesses and inquire about telephone charges and detailed bills in Internet cafes, mobile phones, WeChat halls and your own business halls in the future. Any business instructions sent by China Unicom to 100 10 are free, and there is no short message fee.