Humanity has not yet adjusted to current phone technology.
If you have an answering machine, you gain NOTHING by answering a phone just because it happens to ring. You can screen the call with your machine, and then answer the phone if you want to deal with the caller and his issue now.
I'm sure that in a few years almost everyone will do this. Employing this technique, there is little or no need for Caller ID. One is immune from telephone salespeople. There is no negative. Nothing is lost.
I would even suggest that your answering machine's outgoing message be something like:
"Thanks for calling, messages for Joe Blow can be left at the tone, this phone is ALWAYS answered by this machine."
With such a message, you're being honest about what is going on, and letting telemarketers know that it is hopeless for them. If enough people did this, the telemarketing industry might disappear.
(I'd sure love such a perfect a solution to junk email, and the solution to junk snail mail requires calling just about everyone, since the United States lags so far behind much of Europe in privacy protections, with a current administration which would outlaw privacy totally if it could.)
On the subject of phones, I'd also like to point out some other things: