The Dallas Court of Appeals held that a pro se letter from an Illinois resident denying liability and requesting an extension of time to retain counsel and file a "complete answer" waived the defendant’s subsequent special appearance.  The defendant argued that the letter did not consitute an answer.  The court held that  the letter constituted an answer.  Because an answer constitutes a general appearance, the court held the defendant waived any challenge to the trial court’s personal jurisdiction.  The court’s opinion in Triad Realty Servs., Ltd. v. Green can be found at this link.