try installing aeb button (
http://ae.inc.ru/aebplus.php). it will allow you to set the end call button to "do nothing" or something like that.
if that doesn't work maybe try flashing a custom rom (this would only work if its a software problem and not an actual hardware problem). moreover if your running the stock rom make sure you unlock your phone before flashing a custom rom (if you chose to do this but try aeb button first).
good luck
