| Abbreviation | Definition |
|---|---|
| ISP | Internet Service Provider |
| ISSI | Inter-Switching System Interface |
| ISSIP | Inter-Switching System Interface Protocol |
| ISSP | Interim Interswitch Signaling Protocol |
| ISTD | International Subscriber Trunk Dialing |
| ISUP | International Standards Telecommunications Union |
| ITA | Illinois Telecommunications Association |
| ITA | Industrial Telecommunications Association |
| ITA | Inferior Telecommunications Apparatus |
| ITC | Interstate Telecommunications Cooperative |
| ITCC | Information Technology and Communications Complex |
| ITEC | Internet Telecom and Electronic Commerce |
| ITFS | International Toll Free Services |
| ITNL | Indusind Telecom Network Ltd |
| ITNR | Information and Telecommunications Needs Research |
| ITO | Institute for Telecom Organization |
| ITP | Interactive Telecommunications Program |
| ITP | Interdisciplinary Telecom Program |
| ITP | Internet Telephony Processor |
| ITR | International Telecommunication Regulations |