The approval by CFIUS was the last outstanding regulatory authorisation required to complete the transaction.
Antitrust clearance decisions have previously been obtained for the transaction from antitrust authorities in China, Germany, Hungary, South Korea and the United States.
IDT stockholders have previously voted to adopt the merger agreement and approve the transaction at a special meeting of stockholders held on January 15, 2019.
All necessary regulatory approvals for the acquisition have now been received and the transaction is expected to complete on March 29, 2019 Pacific Daylight Time, March 30, 2019 Japan Standard Time, subject to customary closing conditions.