I have both acted as a reference and had my references called. In my experience, references are only called after a person has been interviewed (at least once), immediately before a final offer is made. No one wants to have their professional references having to field a bunch of phone calls, so they expect that the companies they contact will be serious about offering them a job before that happens. The references are not to generate interest in you, they are to confirm that the company's interest in you is well-founded.