Quickly Silence iPhone Duo Without a Ring/Mute Switch

The new iPhone Duo drops both the classic Ring/Silent switch as well as the newer Action button, so there is no physical mute control on the device, and no way to assign the Silent Mode control to another button. That said, you can still silence the device pretty quickly – you just do it on-screen instead using a new way to invoke Control Center. With your device unlocked, open Control Center by tapping the circular "status bar" icon, then tap the Silent Mode button (the bell icon).