There is a white note on the SMS interface of iphone4.

I don't know what a white strip is like. One possibility is that you sent it to the same person. Send too much. There are a lot of chat records. You deleted that message. Send it to that person again and try. ...

Mine is the same. Because I sent a lot of messages to the same number and saved them there. ...

If it doesn't work ... after you switch programs and interfaces or even shut down and restart, see if the white line still exists. If it still exists, it is a hardware problem. There is something wrong with the display screen or screen line. You have to repair it. ...