[weezyfeezy]

Same thing on mine...it seems like it could be the plastic faceplate over the LCD screen that causes the problem. On mine at least, when you apply a little pressure at the base of the faceplate (over the sprint logo @ center) and at the top of the screen (near the speaker), the oily appearance recedes...only to return when you release the pressure. Maybe a manufacturing defect where the faceplate wasn't fastened to the phone properly.

I had the sprint people tell me everything from "it must be your dirty fingers" to "the screen absorbs sweat from your face...I used to be a tech, I know these things." Pretty annoying, but not worth $50 to replace so long as the phone keeps working.