iPhone handset speaker has broken - any chance of replacing for a white iPhone?

Today my iPhone speaker at the top of the phone for calls has stopped working. I am not sure why, the speakerphone still works and so does the headphones that came with the iPhone. People can hear me, but I just can't hear them.

I was planning to go to the Apple store tomorrow about this, but does anybody know how I can fix this myself?

And also if I do get a replacement at the Apple store, is it possible to change my black iPhone for a white iPhone?