setStyle("borderStyle", "none");

http://www.actionscript.org/forums/showthread.php3?t=40725
http://www.actionscript.org/forums/showthread.php3?s=&threadid=39683&highlight=textArea+style+global

http://www.actionscript.org/forums/showthread.php3?s=&threadid=39572&highlight=textArea+style+global

Posted by Flexagon . .