You can't mute an iPhone?!
I just saw this Kickstarter project and was totally stunned. It's a little bit of hardware to put your iPhone in silent mode.
It's called the Mutator and you plug it into your iPhone to mute everything:
Having never owned an iPhone I didn't realise you couldn't do that, I can barely believe it as on Android it takes about a second to mute everything.. Perhaps some of you iPhone users would love it though! :)