I initially thought the included headset was broken, because the volume rocker didn't return to its centre position. It turned out to be a potentiometer with very short throw, so works as it should, but that was not obvious to me. Especially since it was marked +/- rather than with the usual wedge-shaped crescendo symbol.

Perhaps also mention that the headset won't control the volume setting on the phone, as this might be the expectation people have coming from other phones/headsets. (So, you can't raise volume above what is already set on the phone.)