How to cancel sending SMS and MMS by mobile phone?

Processing method of converting SMS sent by Android phone into MMS: 1. Check whether the "Subject Bar" is open in the SMS editing interface, and press the menu key to close it; 2. Enter the SMS settings to see if there is an option of "converting SMS to MMS" and close it; 3. Enter the SMS settings to see if there is an option of "Remind when SMS is converted into MMS" and turn it on. Then short messages sometimes have too many words, and they will also be converted into MMS. We should pay attention to these.