##### 



Exhibit 21

Subsidiaries of the Registrant

|                                      |  |             
|------------------------------------- |  | ------------
|XO Communications, Inc. Subsidiaries: |  | Jurisdiction
|                                      |  |             
|ITC                                   |  | Utah        
|LHP Equipment, Inc.                   |  | Delaware    
|XO Alabama, Inc.                      |  | Washington  
|XO Arizona, Inc.                      |  | Washington  
|XO California, Inc.                   |  | Washington  
|XO Capital, Inc.                      |  | Washington  
|XO Colorado, LLC                      |  | Washington  
|XO Connecticut, Inc.                  |  | Washington  
|XO Data Services, LLC                 |  | Delaware    
|XO Delaware, Inc.                     |  | Washington  
|XO Domestic Holdings, Inc.            |  | Delaware    
|XO D.C., Inc.                         |  | Washington  
|XO Florida, Inc.                      |  | Washington  
|XO Georgia, Inc.                      |  | Washington  
|XO Hawaii, Inc.                       |  | Washington  
|XO Idaho, Inc.                        |  | Washington  
|XO Illinois, Inc.                     |  | Washington  
|XO Indiana, Inc.                      |  | Washington  
|XO Interactive, Inc.                  |  | Washington  
|XO Intercity Holdings No. 1, LLC      |  | Washington  
|XO International Holdings, Inc.       |  | Delaware    
|XO Kansas, Inc.                       |  | Washington  
|XO Kentucky, Inc.                     |  | Washington  
|XO LMDS Holdings No. 1, Inc.          |  | Nevada      
|XO Long Distance Services, Inc.       |  | Washington  
|XO Louisiana, Inc.                    |  | Washington  
|XO Maine, Inc.                        |  | Washington  
|XO Management Services, Inc.          |  | Washington  
|XO Maryland, LLC                      |  | Washington  
|XO Massachusetts, Inc.                |  | Washington  
|XO Michigan, Inc.                     |  | Washington  
|XO Minnesota, LLC                     |  | Washington  
|XO Mississippi, Inc.                  |  | Washington  
|XO Missouri, Inc.                     |  | Washington  
|XO Nevada Merger Sub., Inc.           |  | Delaware    
|XO New Hampshire, Inc.                |  | Washington  
|XO New Jersey, Inc.                   |  | Washington  
|XO New Mexico, Inc.                   |  | Washington  
|XO New York, Inc.                     |  | Washington  
|XO North Carolina, Inc.               |  | Washington  
|XO Ohio, Inc.                         |  | Washington  



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##### 



|                                                     |  |               
|---------------------------------------------------- |  | --------------
|XO One, Inc.                                         |  | Delaware      
|XO Oregon, Inc.                                      |  | Washington    
|XO Pennsylvania, Inc.                                |  | Washington    
|XO Rhode Island, Inc.                                |  | Washington    
|XO Services, Inc.                                    |  | Delaware      
|XO South Carolina, Inc.                              |  | Washington    
|XO Tennessee, Inc.                                   |  | Washington    
|XO Texas, Inc.                                       |  | Washington    
|XO Utah, Inc.                                        |  | Washington    
|XO Virginia, LLC                                     |  | Washington    
|XO Washington, Inc.                                  |  | Washington    
|XO West Virginia, Inc.                               |  | Washington    
|XO Wisconsin, Inc.                                   |  | Washington    
|40% Interest in
Telecommunications of Nevada, L.L.C. |  | Delaware      
|                                                     |  |               
|XO Domestic Holdings, Inc. Subsidiary:               |  | Jurisdiction  
|XO Mindshare, LLC                                    |  | Washington    
|                                                     |  |               
|XO International Holdings, Inc. Subsidiaries:        |  | Jurisdiction  
|XO International, Inc.                               |  | Delaware      
|Nextlink Global ASP                                  |  | Denmark       
|                                                     |  |               
|XO Management Services, Inc. Subsidiary:             |  | Jurisdiction  
|XO Management Services Nevada, Inc.                  |  | Washington    
|                                                     |  |               
|XO Intercity Holdings No. 1, LLC Subsidiary:         |  | Jurisdiction  
|XO Intercity Holdings No. 2, LLC                     |  | Delaware      
|                                                     |  |               
|XO Long Distance Services, Inc. Subsidiary:          |  | Jurisdiction  
|XO Long Distance Services (Virginia), LLC            |  | Washington    
|                                                     |  |               
|NEXTLINK Global AsP Subsidiaries:                    |  | Jurisdiction  
|Nextlink Belgium, SRLP                               |  | Belgium       
|Nextlink France, SAS                                 |  | France        
|Nextlink Deutschland, GMBH                           |  | Germany       
|Nextlink Netherlands, B.V                            |  | Netherlands   
|Nextlink United Kingdom, Ltd.                        |  | United Kingdom
|                                                     |  |               
|XO Nevada Merger Sub., Inc.:                         |  | Jurisdiction  
|50% Interest in
Telecommunications of Nevada, L.L.C. |  | Delaware