| U.S. Companies | ||
| AT&T | Verizon | CenturyLink |
| FairPoint Communications | Hawaiian Telecom | Windstream Communications |
| Surewest Communications | SBC | U S WEST / Qwest |
| Ameritech | GTE | BellSouth |
| New England Telephone | Southwestern Bell | Southern New England Telephone |
| C&P of Maryland | C&P of Virginia | Pacific Bell |
| Alltel Communications | Shenandoah Telephone | Citizens Utilities of California |
| Fairbanks Municipal Utilities | Cincinnati Bell | Continental Telephone |
| Rochester Telephone | Centel | New Jersey Bell |
| Roseville Telephone | Illinois Bell | United Telephone |
| Frontier Telephone Company | Alaska Communication Systems | Pan American World Airways |
| Nevada Bell | South Central Bell | Sprint |
| International Companies | ||
| Bell Canada | SaskTel | Telia (Sweden) |
| Elisa (Finland) | CANTV (Venezuela) | CODETEL (Domenican Republic) |
| Korea Telecom | Hondutel | Panama Canal Commission |
| Equatorial Guinea | Jamaica | Puerto Rico Telephone |
| Columbia | Ministry of Communication (Kuwait) | Cable and Wireless (Barbados) |
| Manitoba Telephone | Zambia | |