What is the number of the modified SMS center? How to modify it?

SMS-SMS Settings-Mode Settings-There are four modes (different phones may be different). The first one is used to send short messages. If you change it, you can't send text messages. I really want to change my suggestion and record the original figures to prevent them from being lost (plus sign is indispensable). The other three modes are empty at first. By the way, if you want to change them, just change the mode directly, if you have four modes. You can change it any way you want next.

In addition, if you change it, you can't deduct money from playing mobile games registered by SMS. If you still don't know, you can tell me.