Hence the simple interface on their iPhone earbuds:
Press once to answer a call.
Press twice to send the call to voicemail.
Press once to hang up.
Press once to hold the current call and switch to new call.
Hold for 2 seconds and release to ignore the new call.
When listening to music:
Press once to play or pause a song.
Double-click to skip to the next song.
Triple-click to return to the previous song.