I can't explain all possible reasons, but try this article so that you can instead perhaps get some understanding as to "how this touch screen stuff works:

http://electronics.howstuffworks.com/iphone1.htm

milo

Thanks every one. The information is useful.

sorry to hear that. but industry experts predicted such defects on touchscreens to surface soon. they call it the "dead strip". according to them, it was bound to happen after iPhone bought the technology from a Finnish firm.

I guess it's time to buy a non-touchscreen phone.