What do you mean by "Display Subject Bar" and "Number of Characters" in the SMS settings of iphone4?

This is mainly aimed at imessage. When you enable imessage, open the subject bar, and two lines will appear in your information input box. The first line is the subject, and the following is the text. The number of characters will be displayed on the right side of the input box.

The subject is similar to email.

Simply calculating the number of characters is to make it easier for you to check whether the content sent will exceed the capacity of the receiver.