Bottom of touchscreen not responding?
I just replaced the screen on my 3Gs and everything went smoothly except now the bottom 3/4" of the touchscreen does not register any touch. The rest of the touchscreen works fine.
edit: it appears now to work but requires a lot of pressure... again, the rest of the touchscreen is fine.
perhaps the glass is not seated correctly?
an iPhone touch screen should never need any pressure - it's not a resistive touch screen - it's capacitive (CLICK for the Wikipedia page)
sending it to apple wouldn't make any sense - the warranty is gone and the would charge a "little" bit more than a new touch screen would cost.
i would check the connectors first, it's also possible that the "touch layer" isn't fitted properly or defective.
the only way to find out is to open the iPhone again