Volume Button Broken. Now What?

I noticed tonight that the bottom volume button on the side of my iPhone 4 is slightly recessed compared to the top volume button. The bottom volume button still works when pressed however I must now push harder in order for it to work. Also this button now only works when the iPhone is naked. With a bumper added the volume button does not work at all.

I'm going to take it in tomorrow to a Genius but I'm curious if anyone here has had the same problem and what they did about it. I should also mention I have not dropped the iPhone once so I don't know why this is happening. Do you think Apple will be nice enough to fix the button on the spot or replace my phone?