EXHIBIT 21 SUBSIDIARIES OF INTERDIGITAL Company State of Incorporation ------- ---------------------- InterDigital Communications Corporation Pennsylvania Digital Cellular Corporation Pennsylvania InterDigital Mobilecom, Inc. New York InterDigital Patents Corporation Delaware InterDigital Technology Corporation Delaware InterDigital SE Asia, Ltd. Pennsylvania InterDigital Telecom, Inc. New York Universal Service Telephone Corp. Nevada USTC Supply Corporation Nevada USTC World Trade Corporation Nevada Wireless Digital Networks, Inc. Pennsylvania InterDigital Finance Corporation Delaware