5. Vary the pitch or tone

5. Vary the pitch or tone of your voice more than you normally would. A slightly higher pitch will communicate excitement, agreement, or enthusiasm. A slightly lower pitch will relay that you are about to make a very important point. Let your tone go up and down a little bit more
that normal. It will keep the interview from sounding stale, as well as keep you feeling enthusiastic and excited about what you’re saying.

6. If you like, you can put a little stuffed animal or picture of someone you love near the phone and look at it while you talk. It will make you relax and feel like you’re talking to a friend. It will also fill your voice with warmth. Remember, whether it’s the supervisor or a CEO who is interviewing you, that person has feelings, just like you.

In fact, 60 percent of interviewers you will talk to have never been trained at all in interviewing. Hundreds of interviewers have confided in me that they actually feel nervous, incompetent, or stressed when conducting interviews.

A little warmth in your voice, generated by looking at something cuddly, funny, or someone you care about, can go a long way to soothing the “rattled” nerves of some interviewers, thereby making the whole tone of
the interview more relaxed for you as well.

Taken from : Fearless Interviewing - How To Win The Job