Hi Niamh,

The screen is made of glass, so it's not impossible to shatter, but it doesn't break easily. I've dropped mine more times that I care to remember, and my screen has not shattered.

As for which to buy, the pre-pay is the full economic cost of the iPhone. With a contract you get the phone subsidised so it's a lot cheaper for you, but, you are tied to a contract.

Hope that helps,

Bart.