There are lots of rules and etiquette that govern different social situations. Even when using various communication media such as the telephone.
If you are the one who is calling, make sure you check the number of the person you are calling so you do not end up dialing a wrong number. Write it down on a piece of paper if it will help you be more certain.
Allow enough rings so the person on the other line can answer before you dial again. No need to wait only two rings and just when the other person is going to pick up, you hang up. The person might get back to what he or she was doing before and then you disturb him or her by dialing again.
Always use polite language. Ask. Do not order other people around. “Hello. This is Mike. May I please speak with Pam?” is definitely better than, “Can you get me Pam?”
Avoid chewing gum or eating when you are making a call. Nobody likes to hear crunching and chewing while conversing over the phone.
If the person you are trying to reach is not available and an answering machine picks up, don’t panic. Just leave a message after the beep (or whatever). Greet the person. Leave your name, the date and time, and then tell him or her to call you. If he or she doesn’t have your name, then you may also leave it. Don’t forget to say, “Thank you.”