Since I work at home, the telephone can sometimes be a distraction. In the middle of a scene that is flowing well, stopping to talk to somebody trying to sell me crap I don't want breaks the rhythm. I don't begrudge them trying to make a living, but I don't like it when they mess with mine. If you are a phone salesperson, you can call somebody else; I lose track of a scene, I have to fix it myself.
I have friends and family and others to whom I am happy to talk, though I might just say "Hey, let me call you back in a little while."
I am on the no-call sales lists, but not everybody observes those.
Some years ago, I found a little phone zap device, and how it works is simple: If you call here and you aren't in the thing's list of numbers, it rings once. Then it says that if you are a salesperson, go away, I don't want to talk to you. If you are not selling something, there is a key sequence you can press and the call will go through.
If you are selling something and you punch through after the zapper told you not to? I will hang up on you with some vigor, probably offering a query about you not being able to hear so well.
My friends and family and folks who have called before and been accepted go into the zapper's memory and when they call, it rings through. So if my phone rings more than once, I usually answer it because it is usually somebody to whom I'm willing to talk.
The zapper has a caller ID and sometimes people who call here have that blocked. If I see a blocked ID, I don't answer it. If you don't want people to know who you are, I understand, but I find it irritating; in the same way I find people who hide behind netnoms on public e-forums so they can be obnoxious without revealing who they are. (Sure, if you are a world-famous somebody who doesn't want to be overwhelmed with fans who recognize you name, that's one thing. But most people aren't.) Lot of shit gets talked online by people who wouldn't say it to your face.
So, if you are somebody who needs to talk to me, and you give me a call, unblock your caller ID. Or leave a message ...