Can I trade my iPhone 4 for another one?

I dropped my iPhone 4 in the toliet. Can I take it back to AT&T (where I got it from) and trade it for a new iPhone 4?

Not for free.
And only if you bought the insurance plan.

If you bought the insurance plan, they can give you a replacement one for $99.

If you didn't, you'll have to buy a new one for $399.