1. No one makes definite plans anymore, and flaking or changing plans isn't so bad because people just call when they're on their way, when they get there, or when they can't get there.
2. People don't say, "Hi, this is _______"; they just say, "Hi," and expect you to know who it is because everyone assumes that everyone else has caller ID.
3. Many people don't leave messages, assuming that you'll see that they called on their missed called list.
Unfortunately while these things are normal to most of the world, I still have a land line (shocker, I know). I can call you before I leave the house or when I get home again, but that's about it. It might take me a minute to recognize your voice because I have no caller ID. And, if you don't leave a message, I have no idea that you called and never will. The End.