Actually, the Do Not Disturb feature you're talking about is one of the coolest features in the new iOS6 operating system for iPhones, because it's exactly what it suggests: An easy way for you to turn off rings, vibrations, notifications and every other way that your phone might disturb you during a meeting, dinner, tryst with someone special, etc. Now that's not a lot different from Airplane mode, frankly, but there are two things with Do Not Disturb that make it a lot better: you can list specific people who can disturb you -- allowing that emergency phone call from a child, for example -- and you can set up a schedule where your iPhone automatically goes into Do Not Disturb mode from midnight to 8am or similar.

In Airplane mode your phone is basically offline and off the grid, so if you did receive a critical phone call from your boss, your spouse, or similar, you wouldn't know about it until you "landed" (e.g., turned off Airplane mode). Appropriate if you're actually on an airplane, but if you really don't want to be disturbed by anyone then I'd suggest just powering down your phone. Scary, but possible. :-)

To turn Do Not Disturb mode on, simply go into Settings on an iOS 6 iPhone and slide the control from "OFF" to "ON:

Now you're in that mode and regular calls, text messages, Facebook notifications, etc, won't interrupt you or cause the phone to notify you. Easy enough.

To tweak the actual settings for this mode, however, and specify a time window during which it automatically enables, tap on "Notifications", immediately below it on the "Settings" window.

You can see how to proceed: Tap on "Do Not Disturb".

As you can see here, I have my own iPhone automatically switch into Do Not Disturb mode at midnight and switch back to regular mode at 7am. That way I can tell my friends "call me, text me any time. It won't wake me up!" and not have to worry about remembering to turn off the ringer at bedtime.

Yes, I could actually power down my phone at bed time, but, um, I don't.

Notice that you can also enable "Repeated Calls", which means that if an unknown number calls you three times, the third time it'll actually ring or otherwise notify you. That way if a loved one ends up at the police station or stranded and using a strange cellphone, you will eventually be able to answer it. So far I haven't had to test this feature out, thankfully!

One more thing to check: "Allow Calls From". Tap on it and you'll see the options:

By choosing "Favorites" I'm basically saying that anyone whom I've added to my call favorites list in the phone app is special and can bother me, even in Do Not Disturb mode. That's six people in my case, so it's pretty straightforward to manage.

If you'd prefer, "No One" is a more restrictive set, "Everyone" means that you're sort of defeating the purpose of Do Not Disturb (but I expect it means everyone that's in your phone book, so an unknown number would still be screened) and if you'd prefer, you can always make a group like "Disturb Okay" and put people who you want to talk with at 3am or in an important business meeting into that group.

However you manage it, I encourage you to check out and use the Do Not Disturb feature. It's a great one and when you don't get awoken at 4am from a misdial, you'll thank me.