1 EXHIBIT 21.1 SUBSIDIARIES OF THE REGISTRANT STATE OR OTHER OTHER NAMES JURISDICTION OF UNDER WHICH INCORPORATION OR SUBSIDIARY DOES NAME OF SUBSIDIARY ORGANIZATION BUSINESS TYPE OF ENTITY ------------------ ----------------- --------------- -------------------------- IXC Communications Services, Inc. Delaware None Corporation IXC Business Services, LLC Delaware None Limited Liability Company IXC International, Inc. Delaware None Corporation IXC Internet Services, Inc. Delaware None Corporation Applied Theory, Inc. New York None Corporation Storm Telecommunications, Ltd. United Kingdom None Corporation The Data Place, Inc. Delaware None Corporation PSINet, Inc. New York None Corporation IXC Leasing, LLC Delaware None Limited Liability Company IXC Communications Services Europe Limited. United Kingdom None Corporation NTR.NET Kentucky None Corporation Telecom One, Inc. Delaware None Corporation Network Evolutions, Inc. Virginia None Corporation Delaware Capital Provisioning, Inc. Delaware None Corporation Eclipse Telecommunications, Inc. Delaware None Corporation MSM Associates, Limited Partnership Delaware None Partnership Mutual Signal Corp. New York None Corporation Mutual Signal Corporation of Michigan New York None Corporation Mutual Signal Holding Corporation Delaware None Corporation Atlantic States Microwave Transmission Company Nevada None Corporation Central States Microwave Transmission Company Ohio None Corporation Telcom Engineering, Inc. Texas None Corporation Tower Communication Systems Corp. Ohio None Corporation West Texas Microwave Company Texas None Corporation Western States Microwave Transmission Company Nevada None Corporation Rio Grande Transmission, Inc. Delaware None Corporation Grupo Marca-Tel S.A. de C.V. Mexico None Corporation Progress International, L.L.C. Texas None Limited Liability Company UniDial Communications Services, LLC Kentucky None Limited Liability Company