Exhibit 21



|                                                  |  |                                       
|------------------------------------------------- |  | --------------------------------------
|Subsidiary                                        |  | State of Incorporation or Organization
|PAETEC Corp.                                      |  | Delaware                              
|PaeTec Communications, Inc.                       |  | Delaware                              
|PaeTec Communications of Virginia, Inc.           |  | Virginia                              
|PAETEC Integrated Solutions Group, Inc.           |  | Delaware                              
|PAETEC Software Corp.                             |  | New York                              
|PAETEC iTEL, L.L.C.                               |  | North Carolina                        
|US LEC LLC                                        |  | Delaware                              
|US LEC Communications LLC (1)                     |  | North Carolina                        
|US LEC of Alabama LLC (1)                         |  | North Carolina                        
|US LEC of Florida LLC (1)                         |  | North Carolina                        
|US LEC of Georgia LLC (1)                         |  | Delaware                              
|US LEC of Maryland LLC (1)                        |  | North Carolina                        
|US LEC of North Carolina LLC (1)                  |  | North Carolina                        
|US LEC of Pennsylvania LLC (1)                    |  | North Carolina                        
|US LEC of South Carolina LLC (1)                  |  | Delaware                              
|US LEC of Tennessee LLC (1)                       |  | Delaware                              
|US LEC of Virginia L.L.C. (1)                     |  | Delaware                              
|Allworx Corp.                                     |  | Delaware                              
|MPX, Inc.                                         |  | Delaware                              
|Technology Resource Solutions, Inc. (2)           |  | New York                              
|McLeodUSA LLC                                     |  | Delaware                              
|McLeodUSA Information Services LLC                |  | Delaware                              
|McLeodUSA Telecommunications Services, L.L.C. (1) |  | Iowa                                  
|McLeodUSA Purchasing, L.L.C.                      |  | Iowa                                  
|U.S. Energy Partners LLC (3)                      |  | New York                              
|PAETEC Realty LLC                                 |  | New York                              
|Quagga Corporation                                |  | California                            
|Cavalier Telephone Corporation                    |  | Delaware                              
|CavTel Holdings, LLC                              |  | Delaware                              
|Cavalier Telephone LLC                            |  | Virginia                              
|Cavalier IP TV, LLC                               |  | Delaware                              
|Cavalier Services, LLC                            |  | Delaware                              
|Elantic Networks, Inc.                            |  | Delaware                              
|SM Holdings, LLC                                  |  | Delaware                              
|Talk America Holdings, Inc.                       |  | Delaware                              
|Access One Communications Corp.                   |  | New Jersey                            
|Compco, Inc.                                      |  | Delaware                              
|Talk America of Virginia, Inc.                    |  | Virginia                              
|Talk America Inc. (1)                             |  | Pennsylvania                          
|LDMI Telecommunications, Inc.                     |  | Michigan                              
|NT Corporation                                    |  | Delaware                              
|TC Services Holding Co., Inc.                     |  | Pennsylvania                          
|Cavalier Telephone Mid-Atlantic, L.L.C.           |  | Delaware                              
|Intellifiber Networks, Inc.                       |  | Virginia                              
|Network Telephone Corporation                     |  | Florida                               
|OmniCall, Inc.                                    |  | South Carolina                        
|The Other Phone Company, Inc.                     |  | Florida                               



|(1) | Doing business as PAETEC Business Services.
|--- | -------------------------------------------



|(2) | Doing business as PAETEC Energy.
|--- | --------------------------------



|(3) | Doing business as PAETEC Energy Marketing Corp.
|--- | -----------------------------------------------