You could take it back to the shop you bought it from if it has a worrenty? Excuse my bad spelling..! You can risk taking it to some guy down your local market? Personally I wouldn't, but it could be a last resort! If its on a contract, I'm sure your provider are able to replace the phone? Good luck :)
If it is under warranty, you can pay to get it fixed. I would personally purchase a replacement screen and fix it myself as I did with an older digital camera.
What if I dont have a warranty?