In order to expedite the proceeding, the court may hold a prehearing conference, at which the petitioner need not be present if he or she is represented by counsel who is present. The conference may be by telephone. Whether held by telephone or in person, the conference shall be stenographically recorded or tape-recorded. At the prehearing conference, the court may order a showing by the petitioner of the materiality of the testimony expected to be presented by any witness subpoenaed by the petitioner, supported by affidavit where appropriate, and, upon petitioner’s failure to show the requisite materiality, may order that the subpoena for such witness not be issued or be quashed.