This isn't a major fix. If you can take it into an Apple Store, a genius should be able to fix this in a matter of a few minutes. If the Genius woke up on the wrong side of the bed that day then you are kind of out of luck. I guess you could try again another day but there's no gaurantee that you won't get the same Genius. If you are good with handy work then you could open the phone up and push the button back out. Since your warranty is already up then you can't void it. There are video on how to open the iPhone on YouTube, but follow the instructions carefully! There are many screws and small parts in the iPhone.
David
