Apple INC. have had over 4000 (Iphone's) sent in when all they needed was to simply be taken apart and the digitizer (touch screen + LCD) needed to be unconnected and reconnected properly. if you knock your phone or its assembled wrong it can simply make it hard for the touch screen to work correctly this is a common mistake! the flux cables are the issue sometimes they don't get a proper connection and therefore the touch screen will sometimes be not very effective and sometimes will randomly stop working, making you have to lock your (Iphone) and try to use it again. locking and unlocking your phone usually would make it work again because it resets the touch timer. We have never had a case where some ones (Iphone) 4 not 4s is broken just because of a dodgy touch screen, if it is stuffing up, you either didn't plug it in properly, the cables are dirty or when you assembled it yourself you damaged the flux cables, thankyou very much and please try this simple method, it is NEVER a broken screen just because it wont touch sometimes. Official apple support crew. NEVER USE A DODGEY, FAKE OR RIP OFF COMPANY ESPECIALLY A CHEAPER VERSION OF APPLE CLAIMING TO BE APPLE!