Try Swipelock, you can find it in Blackberry App World. It locks the screen when the screen saver comes on, it also locks when you press the lock button on the top right of phone and it also locks the screen when a call is connected. You can swipe the bar from left to right to unlock or with a setting you can add a password. I had the same problem, Swipelock will stop the phone from going into Mute/Hold/Speaker mode during call.