My wife's iPhone3G thrown by my son, and the switch physically broken.
I'm Japanese and live in Japan. So I have imported the necessary parts first. After that, Using this site, and one by one to repair. It's a little difficult to repair for me, but finally I was success to fix.
I think most important point is to using double-sided tape.
iPhone 3G Replacement Battery
iPhone 3G/3GS Headphone Jack Assembly
iPhone 4 Replacement Battery