EXHIBIT 99.1(A)—CERTIFICATION OF CHIEF EXECUTIVE OFFICER

Certification Pursuant to

18 U.S.C. Section 1350

(as Adopted Pursuant to Section 906 of

the Sarbanes-Oxley Act Of 2002)

I, James A. Courter, Chief Executive Officer of IDT Corporation (the “Company”), do hereby certify to the best of my knowledge and belief that:

1. The Company’s Annual Report on Form 10-K for the year ended July 31, 2002 (the “Report”) fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934 (15 U.S.C. 78o(d)); and

2. The information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company.

Date: October 29, 2002

/s/    JAMES A. COURTER      

James A. Courter