When I was in college I had a roommate who enjoyed flexing his muscles in the mirror. He could do it for hours at a time. A little vain? Well, I am going to ask you to do the same thing (except leave out the flexing muscles part). In prep for a telephone interview (or any telephone contact), make sure you have a mirror within view. Why? Because I want you to look into that mirror consistently throughout the phone call. And smile. You will improve your telephone presence 110 percent just by using this simple technique. You will find yourself coming across as much friendlier, more interested, more alert. If you are at all self-conscious about seeing yourself in the mirror, you can use the mirror as an occasional checkpoint. But for most of us, seeing oneself reflected back gives us the kind of feedback necessary to make instant modification toward a more positive presence.
Remember, you should be standing, so a wall mirror usually works best. You can pick up a small wall mirror for a limited amount of cash. It's worth it.
Try it the next time you are on the phone. But don't do it with your roommate around.