Leaving a voicemail can still be a good way to grab the attention of a potential new customer. However, when it comes to leaving a voicemail, you only have a few seconds to actually grab the listener's attention. Most salespeople screw this up by leaving too much information and making themselves sound like a salesperson, which is the kiss of death when leaving a voicemail.
Perhaps the biggest mistake in a sales voicemail is pitching too aggressively. If you sound like a smarmy used car salesperson, your prospects are going to delete your voicemails faster than you can say "lowest price guaranteed!"

"When closing your voicemail, say that if you do not hear from them in three days, you promise to call back. Three days later, start your voicemail (or live call if you reach the person) with, 'As promised, I am calling again to share...' Close with, 'If you haven't had a chance to return my call, I promise to call back in two days.' Two days later, call back and open with, 'As promised, I am calling back...' The message you are sending is that you keep your promises!"
Think through what you are going to say before you place the call. When men hear the beep, they often freeze up and forget what they wanted to say. If you want to be the go-to guy at work, then you have to exhibit competence on all levels. Don’t spoil your confident image by hemming and hawing and filling your messages with “uhhhhs,” and “ummmms.” If it’s a really important call, consider writing out what you want to say beforehand. If the person picks up, great, you now have some notes to remember what you wanted to talk about. If they don’t answer, you can leave a clear and concise message.