The N95 is built like a brick. In fact, Nokia extensively torture their phones to minimise the chance of the screen cracking (unlike samsung). As anyone who saw the BBC programme recently, they twist the phones until the battery cover pops off..
What you can't protect any screen from is a knock directly to the screen, this will put presssure on the screen causing a crack. It can happen if you put the phone in a handbag or trouser pocket.
And there is no way it can happen all by itself.