I bought a used iPhone 4 a few weeks ago but just today noticed a small speck of dust under the screen near the bottom(iPhone was rotated to take the attached picture). I was curious to see when my iPhone was made so I looked up the serial number and it turns out it is a refurb and not a used one. It was rebuilt in November 2011 and has an AppleCare warranty until June 2012. Would they even consider replacing it? I know it is small and despite this little speck the phone works great with no stuck or dead pixels or yellowish tint.