I got a set of headphones to review for Amazon.com and they included a volume control on the cord. While I was checking them out with my iPhone, I found the volume control wouldn't control my iPhone. Odd behavior for a brand new set of headphones I thought. When I tried them with my daughter's iPod, they worked fine. So, I realized I had a problem with my iPhone. I did a quick Google search and found the problem.
I carry my iPhone in my pocket and have for years. After all that time, a lint ball had formed in the socket where the headphones plug in. My earphones worked just fine. But, the lint ball was keeping the plug from making contact so that the volume control worked. The solution was extremely simple. I used a bobby pin, as you can see in the picture. But, you could use a toothpick. Be careful digging around inside your iPhone. I was a little nervous. But, I gently removed a major wad of lint. And, voila! The volume control on the headphones worked perfectly.