Currently Being ModeratedSep 15, 2012 10:18 PM (in response to Anna730)
The warrranty covers defects in manufacture. If Apple decides it is due to that and not something you did then they will replace it. We can't say they will or won't and you had best take it in for them to assess.
Currently Being ModeratedSep 15, 2012 10:26 PM (in response to Anna730)
To elaborate on what Limnos said, if the phone shows no signs of accidental damage, this would be covered by the one-year limited warranty (or two-year warranty if you have an AppleCare Protection Plan or AppleCare+). If the repair center or Apple Retail Store determines the issue with the button is due to accidental damage, you would be required to pay the out-of-warranty replacement fee. For the iPhone 4, that fee is currently $149, and for the 4S it's $199. If you have AppleCare+ with one or both of the accidental damage incidents remaining, the repair/replacement fee would be reduced to $49, but it would count as one of the incidents. If you have an Apple Store in your area (http://www.apple.com/retail/storelist/), you should make a Reservation for the Genius Bar to have a look at the phone. That is the quickest way to get a determination on whether it's covered. If not, you may contact AppleCare Support at 1-800-275-2273.
Currently Being ModeratedSep 15, 2012 10:34 PM (in response to Limnos)
Back it up before you take it in. Apple will give you a refurbished unit, they won't repair yours and give it back to you.
Currently Being ModeratedSep 15, 2012 10:38 PM (in response to Limnos)
Here are the instructions for preparing your phone for service or replacement.