Dropped 3GS Phone appears to work just not screen iPhone 3G

I have an iPhone 3GS, its a couple of years old and Ive prided myself on taking extremely good care of it. That being said, I took out my phone today to play Words with Friends when I dropped it. It landed on a tiled floor and bounced a few times. I picked it up and half the screen had gone grey, the other half had lines throughout it.
I took it to my computer and plugged it in. The screen lights up when I press the home button and it vibrates when I get an email/text message and I tried calling the phone and the call goes through and the phone rings/vibrates. I just cannot get the screen to work.
Thoughts on a solution? I would prefer not to pay a ton of money to have it fix as my contract with AT&T is up in June and I want to switch to Verizon.
3GS Mac OS X (10.6.7)