My classmate received a text message from my mobile phone. But I didn't send it.

I once met a situation where the called user received a short message, which showed the number that he had called or sent a short message before, but it was not actually a short message sent to him by this number. This is the problem of PHS terminal. Looking at the calling number of this short message in the short message system, you can see the real number of sending short messages, not the one displayed on PHS. However, this is only a very accidental situation.