The following process requires that you are using iOS 4 or above. Tap on the "Settings" application on the iPhone...

Choose "Messages"...

Set the option "Character Count" to "On" or "Off" depending on your preference...

If you enable the counting of the characters in your SMS message composing, it may not be immediately apparent. This is because at first, no count is shown. Instead, he count only appears at around the 50th character to be displayed. Below you can see an example. I was sating to write the text message "This is an example of how SMS character counting works", but the count appeared as I typed in the last "S" on "SMS". Delete that letter and the count disappeared. Therefore very short messages are likely to show no SMS count...