At the moment my phone can have three states - "Available for calls" (on), "Not available for any calls" (off/airplane mode) and "Divert calls" (which pushes calls elsewhere - by default to answerphone).
What I want is an additional mode "User is asleep, is your call important enough to wake them up?", whereby the call is routed to an automated system which tells people I'm asleep and asks them if they'd like to (a) put the call through anyway, (b) leave me a message on voicemail or (c) just hang up. Said voicemail would not trigger an alert on my phone until I changed mode back to "available".
Additionally while in "Leave me alone" mode all incoming text messages would get an automic response before they were delivered, telling them that I was asleep, and that if they wanted my phone to go "BEEP" then reply "Yes", otherwise the message would be delivered when I wake up.
I know I'm not the only person who would like my family/friends to be able to wake me up at 3am in an emergency, but only if they actually choose to do so. Or, indeed, if I'm in a meeting, having a date with Julie, etc. Most people would, I'd think, happily choose to be polite, and I could have a happy halfway house between "I am completely free to chat to you _right now_" and "I cannot be interrupted, no matter what".
Original post on Dreamwidth - there are comments there.