Hi,
First check that household or bank account insurance does not give cover.
You have a few of options.
1, Fix a screen shield on it to further protect the screen, and this will also mask small cracks.
2, Make an appointment with a Genius Bar at your local Apple Store, where they will be able to give you optons, one being a one off payment for a replacement.
http://www.apple.com/uk/retail/geniusbar/
3, Visit your local o2 High-Street Store to arrange for the phone to be sent off to their repair centre. They will then contact you with a costing to which you can decline the cost or authorise it.
Ensure you carry out a back up to iCloud and or iTunes before you send it away or visit the Apple Store.
