Using a class inside of a class

Can I use another class inside of a function in a class this function process_queue below is inside of a class called class mailer I want to use the phpMailer class inside of this function so I can send email using smtp. Can this be done and is there any information out there on how to do this function process_queue($num=10){

       if (isset($this->db_settings['demo']) and ($this->db_settings['demo'])){
           return;
       }

       $q = $this->ams->db->query("SELECT * FROM {$this->ams->pre}email_queue
                               WHERE queue_state = 0 ORDER BY queue_time_added ASC LIMIT $num");

       while ($row = $this->ams->db->nqfetch($q)){

           $this->to = $row['queue_to'];
           $this->headers = $row['queue_headers'];
           $this->subject = $row['queue_subject'];
           $this->message = $row['queue_text'];

           $updateq = $this->ams->db->query("UPDATE {$this->ams->pre}email_queue SET
                           queue_time_added = queue_time_added,
                           queue_time_sent = NOW(),
                           queue_state = -2 WHERE queue_id = {$row['queue_id']}");

           if (@mail($this->to, $this->subject, $this->message, $this->headers)){
               $result = 1;
           }
           else{
               $result = -1;
           }

           if ($this->ams->settings['email_debug']){
               @mail ($this->ams->settings['site_email'], $this->subject, $this->message, $this->headers);
           }

           $updateq = $this->ams->db->query("UPDATE {$this->ams->pre}email_queue SET
                           queue_time_added = queue_time_added,
                           queue_time_sent = NOW(),
                           queue_state = $result WHERE queue_id = {$row['queue_id']}");
       }

}