Know whom you are calling.
Know as many details as you can about the person you want to talk to. Know his or her name, title, role in the project, history, and anything else you can find out before you pick up the phone. The goal of the call is to get a personal meeting. Personal relationships are not built over the phone. Have a strong hook (something in your portfolio the person you are calling will want to see) that will get you the meeting.