Broken iPhone 4s lock button?

I bought my iphone from at&t last december. My lock button is jammed, I keep a protective case on my iPhone at all times. My lock button just stopped working a couple of weeks ago. I have the one year warranty on my iPhone and it's valid until December 4th. If I bring my phone to the apple store will they replace it? And also, I'm not sure if i still have my receipt or not. Do I have to have it with me for them to do anything?

As to the warranty is one year, Apple should replace it for you.