His iPhone 4S volume buttons did not work at all, his mute switch was unreliable and he was going through earbuds like crazy.
I first tried replacing his volume buttons, hoping for an easier fix but no luck. I bit the bullet and gutted his phone to replace the headphone jack/ volume control cable. It took about two hours, including the amount of time I spent crawling around the floor looking for tiny bits I dropped, twice.
I had to go back into the phone with a q-tip wet with windex to clean the connectors. Be sure to clean the metal parts where the tutorial mentions it. Works perfectly now. Awesome!