| I | In Phase |
| I and Q | In-Phase and Quadrature |
| I/O | Input/Output |
| I/O | Input/Output |
| I/Q | In Phase and Quadrature |
| I2C | Inter Integrated Circuit |
| IAD | Integrated Access Device |
| IAM | Initial Address Message |
| IAS | Integrated Access Service / Internet Access Server |
| IAST | Integrated Access, Switching and Transport |
| IAT | Inter-Arrival Time |
| IBC | Integrated Broadband Communications |
| IC | Integrated Circuit |
| ICD | Internet Call Diversion |
| ICDR | Internet Call Detail Record |
| ICI | Inter Carrier Interference |
| ICL | Intercell Linking |
| ICMP | Internet Control Message Protocol |
| ICNIRP | International Commission on Non-ionsing Radiation Protection International Telecommunications |
| ICP | Integrated Communications Provider / Intelligent Communications Platform |
| ICS | Integrated Communications System |
| ICW | Internet Call Waiting |
| IDC | Internet Data Center / International Data Corporation |
| IDE | Integrated Development Environment |
| IDEAL | Improved Dynamic Envelope Amplifier Line-Up (Powerwave) |
| IDES | Internet Data Exchange System |
| IDF | Intermediate Distribution Frame |
| IDFS | Intelligent Dynamic Frequency Selection |
| IDL | Interface Definition Language |
| IDLC | Integrated Digital Loop Carrier |
| IDS | Intrusion Detection System |
| IDSL | Integrated Services Digital Network DSL |
| IDU | Indoor Unit |
| IEC | International Electrotechnical Commission |
| IEEE | The Institute of Electrical and Electronics Engineers |
| IEEE 802.16d | IEEE standard primarily for fixed last-mile and backhaul applications now known as ieee802.16-2004 |
| IEEE 802.16e | Evolution of IEEE802.16d, designed for mobile data transport & transmission to indoor antenna. Now known as ieee802.16-2005 |
| IEEE-SA | Institute of Electrical and Electronics Engineers-Standards Association |
| I-ERP | Integrated Enterprise Resource Planning |
| IETF | Internet Engineering Task Force |
| IF | Intermediate Frequency |
| IFFT | Inverse Fast Fourier Transform |
| IFITL | Integrated [Services Over] Fiber-In-The-Loop |
| IFMA | International Facility Managers Association |
| IFMP | Ipsilon Flow Management Protocol |
| IFOC | Intermediate Frequency On Chip |
| IGMP | Internet Group Management Protocol |
| IGP | Interior Gateway Protocol |
| IGRP | Interior Gateway Routing Protocol |
| IGSP | Independent Gateway Service Provider |
| IHL | Internet Header Length |
| IIP | Third-order Intercept Point |
| IIR | Infinite Impulse Response |
| IIS | Internet Information Server |
| IL | Insertion Loss |
| ILA | In-Line Amplifier |
| ILD | Internal Locking Device |
| ILEC | Incumbent Local Exchange Carrier |
| ILEC | Data Local-Exchange Carrier |
| ILMI | Interim Link Management Interface |
| IM | Unified messaging |
| IM | Intermodulation |
| IMA | Inverse Multiplexing Over ATM |
| IMAPS | International Microelectronics and Packaging Society |
| IMC | Instant messaging and chat |
| IMD | Intermodulation Distortion |
| IMRP | Internet Multicast Routing Protocol |
| IMS | Internet Protocol Multimedia Subsystem |
| IMSI | International Mobile Subscriber Identification |
| IMT | Intermachine Truck / International Mobile Telecommunications |
| IMTC | International Multimedia Teleconferencing Consortium |
| IN | Intelligent Network |
| INAP | Intelligent Network Application Part |
| INAP AU | INAP Adaptation Unit |
| INE | Intelligent Network Element |
| InfoCom | Information Communication |
| INL | Integral Non Linearity |
| INM | Integrated Network Management |
| INMD | In-Service, Nonintrusive Measurement Device |
| InP | Indium Phosphide |
| INT | [Point-To-Point] Interrupt |
| InterNIC | Internet Network Information Center |
| IntServ | Integrated Services |
| IOF | Interoffice Facility |
| IOS | Intelligent Optical Switch |
| IP | Internet Protocol |
| IP3 | 3rd Order Intercept |
| IPBX | Internet Protocol Private Branch Exchange |
| IPcoms | Internet Protocol Communications |
| IPD | Integrated Passives Device |
| IPDC | Internet Protocol Device Control |
| IPDR | Internet Protocol Data Record |
| IPe | Intelligent Peripheral |
| IPG | Intelligent Premises Gateway |
| IPO | Initial Placement Offering |
| IPOa | Internet Protocol Over ATM |
| IPQoS | Internet Protocol Quality of Service |
| IPSec | Internet Protocol Security |
| IPTel | IP Telephony |
| IPv6 | Internet Protocol Version 6 |
| IPX | Internet Package Exchange |
| IQ | In-phrase and Quadrature |
| IR | Infrared |
| IrDA | Infrared Data Access |
| IRU | Indefeasible Right To User |
| IS | Interim Standard |
| IS-136 | Interim Standard-136 |
| IS-533 | Interim Standard-533 |
| IS-54 | Interim Standard-54 |
| IS-95 | Interim Standard-95 |
| ISA | Industry Standard Architecture |
| ISAPI | Internet Server Application Programmer Interface |
| ISC | Integrated Service Carrier / International Softswitch Consortium |
| ISDF | Integrated Service Development Framework |
| ISDM-PRA | ISDN Primary Rate Access |
| ISDN | Integrated Services Digital Network |
| ISDN-BA | ISDN Basic Access |
| ISEP | Intelligent Signaling Endpoint |
| ISI | Inter Symbol Interference |
| IS-IS | Intermediate System to Intermediate System |
| ISM | Industrial, Scientific and Medical Radio Bands |
| ISO | International Standards Organization |
| ISOS | Integrated Software On Silicon |
| ISP | Internet Service Provider |
| ISUP | ISDN User Part |
| ISV | Independent Software Vendor |
| IT | Information Technology / Internet Telephony |
| ITN | Impedance Transforming Network |
| ITS America | Intelligent Transportation Society of America |
| ITSP | Internet Telephony Service Provider |
| ITTP | Information Technology Infrastructure Library |
| ITU | International Telecommunication Union |
| ITU-T | ITU-Telecommunications Standardization Sector |
| ITV | Internet Television |
| IVI | Intelligent Vehicle Initiative |
| IVR | Interactive Voice Response |
| IVRU | Interactive Voice-Response Unit |
| IWF | Interworking Function |
| I-WLAN | Industrial wireless local area network |
| IWPC | International Wireless Packaging Consortium |
| IWU | Interworking Unit |
| IXC | Inter-exchange Carrier |