You can check online to see when ur warranty expires. I doubt they will exchange it unless u there is something else wrong with the phone that is not drop related. (kind of hard to prove you didn't break it by dropping if ur phone is in very bad shape)
anyways I'm about to go to apple store dt to get mine look at. Mine warranty expire in aug. I have dust + dead pixel. Already unjailbroken. Hopefully they will get me a brand new replacement, although from wat I've read on hofo they are now doing in store screen repair
EDIT: yea just got the display, did it in less than 10 mins. there was another guy with a ipod touch that is very beat up. he claims the speakers wasn't working the genius didn't even check and gave him a replacement out right