Don't ask for a callback. Instead, say when you'll be calling back and make sure that you call back exactly on time. Don't try to sell yourself over the phone. The purpose of your call should be to schedule an interview so that you can sell yourself in person. Make the call as brief as possible, set the appointment and then hang up.
Community service can reap unexpected rewards.
You may discover opportunities you had never considered before. You may also discover personal strengths and abilities you have never explored. By reaching out to others in your field of interest, you are getting your message out to the right audience. Joining a professional association in your industry may open the door for you to the job of your dreams. It is the ultimate compliment to the employer.