Dov Frankel, explaining something that confused me during the week’s episode of The Talk Show:
Basically, the iPhone has two different volume levels: your ringer
volume, and your audio playback volume. When audio is playing, or
when an audio-centric app is open, the hardware volume buttons
change the volume of the audio. When at the home screen with no
audio playing, the volume buttons change the ringer volume. The
audio level can go to 0, but the ringer volume can only go to 1.
To turn the ringer off, you have to use the hardware switch.