There was an annoy fleck of dust on the inside part of the screen on my N-Gage QD. I was trying to find out how to get the damned faceplate off of the QD in order to blow some air over the screen to get the dust off. It's not in the manuals! Oi. But, with a bit of searching around (and I found some good forums for Symbian and N-Gage stuff) I found my answer. This is just for my own documentation for when I need to change the faceplate of the QD, but if it helps you too, here is the answer from a helpful soul at the All About Symbian forums:
The QD's cover is only held by the two clips you see behind the battery cover. Remove the battery and cover. Push on the two clips a bit to disengage the top part of the cover. Now turn the QD over, keypad side up. Then, holding only onto the rubber edge, push down hard on the four-way controller, you'll hear a small click and the left side will open up, then do the same thing on the right side, pushing down on the number pad in the area corresponding to the directional pad (2/3/5/6 area) until you hear the click...And how to get the cover back on:
Looking at the front of the phone (keypad), pull the rubber flaps out of the way with your fingers for the power flap, and your thumbs for the card flap. Line everything up, and push down. It should give you a few solid clicks as you press together the front and back around the edge. And then of course put your battery back in and replace the cover.