Phone Etiquette

Technology seems to have killed phone etiquette.

While etiquette is not something that I am overly concerned with, I can't help but to be appalled by what has become acceptable:

-A call comes in from I-know-not who and the caller says, "Hey."
I don't even know who it is, but clearly I'm supposed to. Caller ID is not necessary, except when I get a phone call like this. Which happens more often than it should.

-I've gotten lots of phone calls from people who say stuff like, "I don't know who I'm calling, but I missed a call from this number."
If it was important, I will call you back. Or someone else used my phone and I don't know what you're talking about.

-Last night (and this is what prompted this post), I got a text from someone that read: "Who is this?"

I realize that phone etiquette is going to change as technology changes, but some of this stuff is just rude.
I also realize that this makes me sound old.
Screw it: I am old (relatively speaking, of course).

I have tried to teach my children good phone manners, but they are convinced that I am a dinosaur. To them, it's perfectly acceptable to grunt as a greeting and they expect a phone call back from someone they called even if they didn't leave a message. As a matter of fact, leaving a message is uncool - the person you're calling already knows who it is, or at least your phone number.

Generational differences widened by technology. How far do I lean in toward the gap? I won't jump over, but obviously a certain amount of understanding is required.
On both sides.