
<TABLE> <S> <C>

<PAGE>
 
<ARTICLE> 5
<LEGEND>
THIS SCHEDULE CONTAINS SUMMARY FINANCIAL INFORMATION EXTRACTED FROM IDT'S FISCAL
1998 FINANCIAL STATEMENTS AND IS QUALIFIED IN ITS ENTIRETY BY REFERENCE TO SUCH
FINANCIAL STATEMENTS.
</LEGEND>
       
<S>                             <C>
<PERIOD-TYPE>                   YEAR
<FISCAL-YEAR-END>                          JUL-31-1998
<PERIOD-START>                             AUG-01-1997
<PERIOD-END>                               JUL-31-1998
<CASH>                                     115,283,519
<SECURITIES>                                60,308,768
<RECEIVABLES>                               44,292,974
<ALLOWANCES>                                 6,255,000
<INVENTORY>                                          0
<CURRENT-ASSETS>                           227,867,064
<PP&E>                                      91,475,613
<DEPRECIATION>                              16,143,137
<TOTAL-ASSETS>                             417,196,204
<CURRENT-LIABILITIES>                       61,486,518
<BONDS>                                              0
<PREFERRED-MANDATORY>                                0
<PREFERRED>                                          0
<COMMON>                                       228,489
<OTHER-SE>                                 238,519,583
<TOTAL-LIABILITY-AND-EQUITY>               417,196,204
<SALES>                                    335,372,915
<TOTAL-REVENUES>                           335,372,915
<CGS>                                      240,859,809
<TOTAL-COSTS>                              339,118,673
<OTHER-EXPENSES>                                     0
<LOSS-PROVISION>                                     0
<INTEREST-EXPENSE>                           5,978,760
<INCOME-PRETAX>                            (4,038,352)
<INCOME-TAX>                               (1,671,000)
<INCOME-CONTINUING>                        (6,263,021)
<DISCONTINUED>                                       0
<EXTRAORDINARY>                              (132,376)
<CHANGES>                                            0
<NET-INCOME>                               (6,395,397)
<EPS-PRIMARY>                                   (0.22)
<EPS-DILUTED>                                   (0.22)
        

</TABLE>
