Even after all this time since the iPhone was launched in the US, and we are still learning things about the phone itself. The iPhone appears to feature a Water Sensor in the Jack port. This feature has also been noticed on the new iPod Touch,
If you look at the headphone jack at the top of the iPhone or the bottom of the iPod Touch, then you will see a white disc - this is the Water Sensor. It changes colour when water has go into your iPhone so there is no need to take apart your device to find out.