Convert BR tags to newlines.

br2nl.php

<?php

/**
 * Convert BR tags to newlines and carriage returns.
 *
 * @param string $string
 *   The string to convert
 *
 * @return string 
 *   The converted string
 */
function br2nl($string) {
    return preg_replace('/\<br(\s*)?\/?\>/i', PHP_EOL, $string);
}