[eluser]wiredesignz[/eluser]
My 2c.
@xwero: echoing TRUE always displays as 1
@Final: You will find the error messages in system/language/english/validation_lang.php, you could create your own version of these in application/language.
Callbacks are never run for an empty input. So `trim|required` is your only choice, unless you create a MY_Validation extension.