I need iphone help, please!?

last night i went to a concert and it rained, no it poured. my iphone 3gs isn't working right anymore. it had the itunes 4 update with iphone 4 capabilities. so i'm using an old one now and put my sims card in it. it put all my things on it but it won't give it the update with the iphone 4 capabilities. it says on itunes that its updated though. any ideas what to do?