After I got some problems with my function to convert a BB-text into HTML. Long words didn't really fit into the layout and only wordwarp() also added breaks to words which would fit into the layout or destroy the other HTML-tags....
So this is my solution. Only words with strlen() >= 40 are edited with wordwarp().

<?php
function bb2html($bb) {
        $words= explode(' ', $bb); // string to array
    foreach ($words as $word) {
        $break = 0;
        for ($i = 0; $i < strlen($word); $i++) {
            if ($break >= 40) {
                $word= wordwrap($word, 40, '-<br>', true); //add <br> every 40 chars
                $break = 0;
            }
            $break++;

        }
        $newText[] = $word; //add word to array
    }
    $bb = implode(' ', $newText); //array to string
    return $bb;
}
?>