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                                                                    EXHIBIT 23.1
 
                        CONSENT OF INDEPENDENT AUDITORS
 
    We consent to the references to our firm under the captions "Selected
Consolidated Financial and Operating Data" and "Experts" in Amendment No. 1 to
the Registration Statement on Form S-4 and related Prospectus of IDT Corporation
for the registration of $100,000,000 8 3/4% Senior Notes due 2006 and to the
incorporation by reference therein of our report dated September 25, 1997 with
respect to the consolidated financial statements and schedule of IDT Corporation
included in its Annual Report (Form 10-K) for the year ended July 31, 1997,
filed with the Securities and Exchange Commission.
 
                                          /s/ Ernst & Young LLP
 
New York, New York
June 4, 1998
