iFixit

Separating the front and back case.

There's a headphone jack cable to disconnect before you can completely remove the back panel.

The headphone jack is recessed into the case, so most headphone jacks won't fit without an adapter (even if they're the right 1/8" plug).

Apple did this to reduce the strain on the narrow metal jack when you yank on the headphones. With this design, the hard plastic cable jacket absorbs most of the impact.

The headphones have a microphone built in, with a button that you pinch to answer a phone call.