A good selling voice is key when making cold calls. You don't want to sound like you don't know what you're talking about, but you also want to seem friendly and approachable. Record yourself doing a sample call, and replay to hear how approachable you sound on tape. This is the best way to measure your voice since most people cannot accurately hear the way their voice sounds. Record yourself a few times, making sure you sound upbeat. Experiment with smiling while talking to see how this raises the tone of your voice and makes you seem friendlier.

Speak Clearly
Do not rush through your sales pitch. People are not going to be inclined to purchase a product or donate to your company if they can't hear what you're saying the first time. Make sure your speed is slow, but not so slow that it is condescending.

Get to the Point
Keep your phone calls short---under four minutes. Cut to the chase within the first 45 seconds of the call. Most people are not willing to spend more than five minutes on the phone with a telesales agent.

Be Prepared for Rejection
People will hang up on you or sometimes yell at you---these are hazards of the trade. Some people feel that telesales calls invade their privacy. Others will not be interested in investing time or money with your organization or product. Expect rude remarks and hang-ups. Their rude attitude is their problem and not yours. Brush it off, and use all your energy on your next sale.

Write a Script
Come up with a script for your calls. You don't need to read it word for word, but knowing what you will say prevents "ums" and long silences. A script to refer to will help you feel more relaxed. Structure each call similarly so you're able to find a flow.

Let Them Talk
If the person on the other end has something to say, listen. At various intervals, let him know you are listening by saying things like "Yes," "mm-hmm" and "I understand." Always use a person's name when making a call to give a more personal touch, especially if he is a regular subscriber or donor to your organization.

Source: Anna Scanlon link