Sending an email to each prospect before you call gives them an additional way to get in touch with you when they're ready. As you're leaving your voicemail, mention that you've sent them a quick email as well that has further details on who you are and the purpose of your call. As Florin Tatulea of Loopio explains:
Now, for today’s lesson, I want to answer three questions about voicemail in English. Here’s what you’re going to learn: Basic rules to follow for voicemail. What you should and shouldn’t say when you leave a voicemail with some examples. What you should include in your own voice message for those moments when you can’t get to your phone.

6. After the message has played, you’ll be given some options for what to do with the message e.g. delete or save it, etc. along with the corresponding number to press.
People tend to remember the first and last events of the day. Now, you could make your sales calls in the morning, but nobody wants something else on their plate when they’re just starting their workday. By waiting until the end of the workday, though – traditionally, around 4:30 p.m. – you won’t be competing with other distractions, and you’ll be one of the last things that happened to the contact while they were at work.