Very few people have my cell number. I can also set up call forwarding to and from home if I want (all part of packages so the cost is low for both). This way I have a reasonable expectation that the call might actually be worth answering, but I can be in touch most all of the time.
I know how to turn it off and not just silence the ringer. When I am someplace I don't want to or cannot be interrupted, I just turn it off and let the system deal with it.
I love Caller ID. Even if the cell phone is on, I can see if it is worth taking the call. Or not.
I really love Voicemail. I figure that if they really have something important to say, it is worth leaving a message. If they don't, I figure it must be low priority.
With a few options and an extra piece of equipment or two, I can be in contact most places. By using the way things are set up I can control the level of interruptions and even control the amount of control people would like to think they have.
Even with all that and the way I use the phone I still find that only one out of maybe twenty calls are worth taking. Therefore, my two favorite phrases, even for stuff at home, have become "It can wait" and "Go ahead. You can deal with it."