Try Apple, and chances are they give you the old $169 to exchange for a refurbished phone. Although, on rare occasions they do that swap for free under warranty, even if it is drop or water damage.
If it was just the screen, I would say fix it yourself (
http://www.ifixit.com/iPhone-Parts/i...-ATT/IF182-003) as it is a very simple fix, but who know what else is damaged.