I love the convenient iPhone headphone controls for starting and stopping playback or adjusting the volume. In addition to the headphones that come with the iPhone, many third-party headphones, including my Etymotic HF3s, include these controls.
Sometimes, the controls seem to stop working. At first I thought it was my headphones. Turns out, most of the time it’s lint. Some fuzz gets into the headphone jack and prevents part of the plug from making proper contact. It can also prevent audio from making its way to one of the earbuds at times.
Easy fix: unwind a paper clip and lightly poke around the jack, pulling the lint outward (it helps to turn the phone upside down, so gravity is helping you).