First, there is no other medium that allows you to convert your confidence that you can create value for your dream client should they agree to meet with you. Your confidence doesn’t come across the same way in an email. Email asks tend to be sterile, devoid of emotion, or too cute for their own good.
Second, and equally important, is the fact that the communication is asynchronous. You can respond to your dream client’s questions and concerns, concerns they are likely to express as a method of getting you off their phone. Because you are on the phone, you have a shot at resolving that concern (provided you have the confidence). An email can be deleted or ignored. Any attempt to resolve a concern can feel like you are arguing.
Third, the key to obtaining commitments is trading enough value in exchange for the time you are requesting. Offers that are spoken with confidence that they deliver value seem to be more effective than offers made over email. If the value proposition for the meeting isn’t exactly right, you have a chance to remedy that with an improvement to your pitch. When what you are selling is a meeting, there must be something that makes it worthwhile for your prospective client.
Finally, your voice is unique to you. It can identify you, transforming you from a first and last name into a human being. Not only can the client hear your voice, they can get a sense of you as a person, what we might call your real voice, or personality if you are willing and able to share that over the phone. All these things are made more difficult over email.
Email is about efficiency. But results in prospecting don’t easily lend themselves to improved efficiency. Results tend to follow effectiveness. If one medium is more effective, using it more often is a better choice than looking for shortcuts.