Most buttons are just asking to be pressed—except those red buttons found on 800 lb. robo-gorillas. Don't press those… Tempt yourself with a button that won't destroy civilization today with our iPhone 3G and 3GS power button.
This button is the external switch used to turn on, turn off, and lock the iPhone.
This is the physical button only and not the button on the iPhone's headphone jack. That part can be found here.
Identify your iPhone
All 3G and 3GS iPhones