Is it possible to set up an iOS 6 device (for example, specifically the iPhone 5, or 3rd generation iPad) such that all the usual sounds from apps and the system sounds like typing or message notifications play when the headphones are plugged in, but when headphones are not plugged in the device is silent?
The silent switch on the left of the device allows one to completely mute (orange in picture below) or unmute all sounds when no headphones are plugged in.
However, when headphones are plugged in, third-party app sounds (e.g.: game music/sfx, video sounds, etc.) will still play through the headphones whether the switch is activated or not.
Unfortunately, there is currently no way to achieve the same behavior for system sounds and Apple apps.
For media sounds, it will use different level when the headphones are plugged in. To do this, you turn down the volume to nothing while an app using media sound is active and your headphone is not plugged in. Plug in your headphone, and you will see that the volume comes back on.
But for notifications and ringtone sounds, it will use same volume regardless of headphones plugged in or not. There are no settings available for differentiating this, I'm afraid.
The headphone port consists of small metal ridges which come in contact with the lines on the connector portion of the headphones.
If these are pushed in it may not be able to emit sound without headphones because it believes headphones are plugged in. Likewise, if the logic board believes these are plugged in no sound will be emitted without headphones either. This is a hardware issue that can be address at Apple Retail or AppleCare
The other potential issue is if Do Not Disturb is enabled, a crescent moon icon will be present by the battery icon, no ringing/notification will occur.