I sent a short message, but it said "SMS not sent". What happened?

If you just sent it, it shows that you didn't send it, and all the numbers can't be sent out, maybe your mobile phone is set incorrectly. I've been in this situation. You call mobile KF to ask, and I just re-pull the card, insert it, and reset the number of the SMS center.

If someone else sends it, she can't send it out, or her number has stopped, which is not your problem.