Hold down the lock button (the button on the top) and the home button at the same time until the iPhone turns off, then it should either restart or you'll have to turn it back on again. If this doesn't work, plug it in to your computer.
i phone screen frozen in enlarged scale ,turning off and restarting doesnt help .the screen returns as normal and then enlarges itself and freezes.syncing to itunes doesnt solve the situation either ...any ideas?