There are several ways to report the screen size of a phone. What I'm interested in is the maximum size in pixels of an image that can be used as wallpaper. However, vendors and phone-related sites have various meanings of screen size:
If your screen size doesn't match what I have, don't quite tell me about it yet. Try to determine what type of screen size you have. If you are using the SysInfo midlet, you should double-check to see if images can be larger than what it reports. In many cases, they can be bigger.
If possible, you should search the manual for your phone. If you get to the gory and boring technical specifications, it often will tell you the maximum displayable image size.
If that fails, you could determine it with trial and error. You should start with an image that is near to what you think your phone accepts. Then adjust the width bigger and smaller to see what the absolute maximum is. Do the same for the height. Be careful and make sure you adjust it slowly. You should get the exact width and height of an image that works, where one extra pixel wide or one extra pixel tall will not fit.
The down side is that the uploader will resize images to be smaller than what it thinks your maximum screen size is. To avoid this, you should use another uploader that doesn't resize images like this one.
This process can take a long time, but the information is very useful and could help out everyone who has the same phone as yourself.