Turn off device volume - iOS

Possible duplicate:
Programmatically disable / disconnect an iOS device?

I need to programmatically disable the device volume. Does anyone know a way?

So far, I have discovered that perhaps I can use the AudioSessionSetProperty () function and use the "kAudioSessionProperty_CurrentHardwareOutputVolume" property, but this property is read-only. I'm not sure if this will work:

float value = 0.0f;
AudioSessionSetProperty(kAudioSessionProperty_CurrentHardwareOutputVolume, sizeof(float), &value);

There are already applications in the App-Store, for example, AutoSilent:

http://itunes.apple.com/nl/app/autosilent/id474777148?mt=8