| AA | Circuit switching |
| A process that, on demand, connects two or more data terminal equipments and permits the exclusive use of a data circuit between them until the connection is released (ISO). |
| AB | SITA |
| Communications number assigned by Societe Internationale de Telecommunications Aeronautiques (SITA). |
| AC | ARINC |
| Communications number assigned by Aeronautical Radio Inc. |
| AD | AT&T mailbox |
| AT&T mailbox identifier. |
| AE | Peripheral device |
| Peripheral device identification. |
| AF | U.S. Defense Switched Network |
| The switched telecommunications network of the United States Department of Defense. |
| AG | U.S. federal telecommunications system |
| The switched telecommunications network of the United States government. |
| AH | World Wide Web |
| Data exchange via the World Wide Web. |
| AI | International calling country code |
| Identifies that portion of an international telephone number representing the country code to be used when calling internationally. |
| AJ | Alternate telephone |
| Identifies the alternate telephone number. |
| AK | Videotex number |
| Code that identifies the communications number for the online videotex service. |
| AL | Cellular phone |
| Identifies the cellular phone number. |
| AM | International telephone direct line |
| The international telephone direct line number. |
| AN | O.F.T.P. (ODETTE File Transfer Protocol) |
| ODETTE File Transfer Protocol. |
| AO | Uniform Resource Location (URL) |
| Identification of the Uniform Resource Location (URL) Synonym: World wide web address. |
| AP | Very High Frequency (VHF) radio telephone |
| VHF radio telephone. |
| CA | Cable address |
| The communication number identifies a cable address. |
| EI | EDI transmission |
| Number identifying the service and service user. |
| EM | Electronic mail |
| Exchange of mail by electronic means. |
| EX | Extension |
| Telephone extension. |
| FT | File transfer access method |
| According to ISO. |
| FX | Telefax |
| Device used for transmitting and reproducing fixed graphic material (as printing) by means of signals over telephone lines or other electronic transmission media. |
| GM | GEIS (General Electric Information Service) mailbox |
| The communication number identifies a GEIS mailbox. |
| IE | IBM information exchange |
| The communication number identifies an IBM IE mailbox. |
| IM | Internal mail |
| Internal mail address/number. |
| MA | Mail |
| Postal service document delivery. |
| PB | Postbox number |
| The communication number identifies a postbox. |
| PS | Packet switching |
| The process of routing and transferring data by means of addressed packets so that a channel is occupied only during the transmission; upon completion of the transmission the channel is made available for the transfer of other packets (ISO). |
| SW | S.W.I.F.T. |
| Communications address assigned by Society for Worldwide Interbank Financial Telecommunications s.c. |
| TE | Telephone |
| Voice/data transmission by telephone. |
| TG | Telegraph |
| Text transmission via telegraph. |
| TL | Telex |
| Transmission of text/data via telex. |
| TM | Telemail |
| Transmission of text/data via telemail. |
| TT | Teletext |
| Transmission of text/data via teletext. |
| TX | TWX |
| Communication service involving Teletypewriter machines connected by wire or electronic transmission media. Teletypewriter machines are the devices used to send and receive signals and produce hardcopy from them. |
| XF | X.400 address |
| The X.400 address. |
| XG | Pager |
| Identifies that the communication number is for a pager. |
| XH | International telephone switchboard |
| The international telephone switchboard number. |
| XI | National telephone direct line |
| The national telephone direct line number. |
| XJ | National telephone switchboard |
| The national telephone switchboard number. |
