You have a Windows Mobile Smartphone C500/Smartphone3/SMT5600 and it has some amount of dust under the screen? Keep reading then.
Jason Dunn, at Smartphone Thoughts, comments "I have an Orange C500, and it's generally a fantastic phone: small size, nice screen, great battery life, Bluetooth, camera, and speedy use. So why do I want to throw it out the nearest window? DUST. It's my second C500, and has a horrible amount of dust under the screen. When I'm using it in direct sunlight the dust lights up and makes the display almost useless. You'd think HTC would have learnt their lesson after the dust problems the original iPAQ had, but it seems not - they continue to make phones and PDAs with insufficiently sealed screens, and dust creeps in."
He has contacted Pocket PC Techs to find a solution for the problem. They discovered the problem: the dust is getting in through the ear piece and side vent. The gasket between the LCD clear cover and the LCD itself is not thick enough, nor does it cover enough at the bottom. HTC quality control at it's finest.
Pocket PC Techs can clean the dust out, but the real solution is a a replacement gasket that is the right size to prevent dust from creeping in again. There's a significant up-front cost to Pocket PC Techs in order to get this gasket made, so they need to know how many people would be interested in this fix before they start.
Jason is running a poll on Smartphone Thoughts to find out how many people are affected and how much would they be willing to pay for a permanent fix - Pocket PC Techs need to know the grounds before some investments. This may be interesting for you.