I respect your honesty. I think a lot of people do the same but would never think of admitting it. I'm not sure why, though. There's nothing wrong with not wanting to be bothered. The more telling thing is that you live in a generational and societal context in which you need to pretend to be busy simply to enjoy something like unstructured solitude, which I think is a perfectly normal and healthy thing to want -- and need -- from time to time.
If I wanted to play two-bit shrink, I suppose I could look for conflicts arising from growing up in a context characterized by both a strong focus on self and compulsory collectivism. Burying one's nose in a phone might represent a socially-acceptable way to remove oneself from that for a while. I know that my younger brothers' adolescent children are not allowed to simply go outside and disappear by themselves for a few hours like I (and my brothers, for that matter) were able to do; so maybe the phone / tablet become a way to do that virtually for the very young that becomes a habit even as they move into young adulthood.
But like most psychological theories, that one would be unverifiable conjecture built on vapor.
I'm semi-retired, have few appointments, and therefore rarely need an alarm. The next time I actually have some place I have to be at some particular time is a dentist appointment in April. But I do keep the BlackBerry by my bed set to the "Phone Calls Only" setting at night. I get almost no wrong numbers, very few people have my cell phone number, and none of my friends or family members who do are prone to drunken, incoherent babbling (at least since Jeannette and I split, and she doesn't have my cell number, anyway); so it's a pretty safe bet that no one will call me at night unless it's actually important.
I really can't expect relatives and close friends to call my "land line" because I don't have one. I have a Magic Jack number that is the only number I give to people and organizations that I never want to hear from, but the ringer is turned off and I never answer it. Everything goes to voice mail (which I rarely bother checking).
Rich