Help iPhone 4 Home Button not working

Hi all,

I have repaired iPhone's for people before WITH much success. But I can't figure this one out for the life of me. It's out of waranty first of all. I've had it about 2 months from the owner so I'd really like to get it back to him.

It was a MESS, got ran over by a truck. Front and back was smashed but phone worked fine! Accept that the back and front was smashed and the home button didn't work.

Replaced LCD screen and back cover, not a problem. Replaced Home button with brand new one, wouldn't work. Replaced dock connector with brand new one, still no activity from the home button. It charges fine and works with iTunes so I know the new dock connector works. I'm at a loss. What else could it be? It's the GSM model. Thanks.