You are finally at the point of making a direct connection with the Hiring Manager. Now what? Your goal should be to set up an interview. No matter how good you sound on the phone, no matter how good you look on paper, you will not get the job without first getting the interview.
Think about the last purchase you made, large or small. Why did you buy the item? Because the benefits were greater than the costs. Simple law of economics. When the benefits outweigh the costs, we buy. In reality, it's not quite that simple. We are actually making the decision based upon the perceived benefits being greater than the perceived costs. Perceptions can be incorrect or incomplete and can also vary from person to person, hence different buying behaviors. Yet it is only when we have a positive perceived benefit/cost comparison that we will make our buying decision.
The same law of benefits versus costs applies to each stage of the employment process. You must convince the employer that the perceived, or potential benefits in hiring you will be greater than the perceived, or potential costs. This applies not only to the hiring decision, but also to whether or not you even get the initial interview. If I, as a Hiring Manager, do not see a benefit in meeting with you (as a potential solution for an immediate or future need) which is greater than the cost of meeting with you (giving up a half hour or hour of my time which could be used for other activities), you will not get the interview. If, however, I see a potential positive benefit/cost ratio, you will get the interview. While you have little control over my perceived costs in interviewing (which relate to the value of my time in other areas of my work), you have almost absolute control over the perceived value of the benefits of a potential interview.
Therefore, you need to think in terms of benefits. Not how you will benefit. Not how much money you want to make. Not what a cushy job it would be for you. That has zero effect on me. If you are going to sell me on interviewing you, you will need to show how you will benefit me and my company.
To make yourself irresistible, you need to focus on what you can do to benefit my company. How you can increase our profits. How you can further develop our product line. How you can increase the efficiency of our existing systems. How you can help our business grow. How you can help our department prosper. How you can make me look good as a manager.
Many students take the attitude that I, as the Hiring Manager, should somehow magically decide what their value is and where they fit into the work world. That is not my job. That is your job. Do not expect me to figure out what your role in life will be. You know you far better than I, so do not expect me to know intuitively and understand your true value, either from the initial call or even after a series of interviews. It is your responsibility to communicate this value.
Interviewing is one of the most difficult activities to conduct in the work world, from either side of the desk. You have a limited time in which to convey value and benefit. And I have a limited time in which to evaluate that potential value and benefit. If you do your job as the transmitter, you will make my job much easier as the receiver.
Know the facts of your personal value and benefit, then sell others on these facts. That is what will make you truly irresistible.