I've had my LG 840G since the end of June and it's been working great until this week.
This Thursday morning I wake up and there is no sound on any of the buttons on the touch screen or the phone itself (I have the sounds set to a volume of 6 or 7). When I make a call, also nothing - I can't hear the person on the other end. That night it managed to fix itself on its own; but yesterday, one moment it is working fine and the next there is no sound again and it has been that way since. The text message function is working fine.