IS-54, an EIA Interim Standard for U.S. Digital Cellular (USDC), is the original TDMA digital standard implemented in 1992. This standard was the first to permit the use digital channels in AMPS systems. It used digital traffic channels but retained the use of analog control channels. This standard was replaced by the IS-136 digital standard in 1996.

The IS-634 interface is a standard defined by TIA/EIA that defines the messaging interface between a TDMA Base Station (BS) and a Mobile Switching Center (MSC). This interface uses the services provided by Connection Oriented SCCP for its transport layer. IS-634 is deployed worldwide in the cdmaOne mobile wireless networks.

IS-661 is a North American standard for 1.9 GHz wireless spread spectrum radio-frequency access technology developed by Omnipoint Corp. IS-661, for which Omnipoint was awarded a pioneer's preference license for the New York City market, is based on a composite of code division multiple access and time division multiple access technologies. The company says IS-661 reduces infrastructure costs and allows higher data speeds than mainstream GSM or TDMA platforms.

IS-95b is an upgraded version of IS-95a for the cdmaOne mobile network that increases the maximum data rate to 115.2 kb/s.

IS-95a, an EIA Interim Standard 95, is the original digital mobile telephony standard based on CDMA technology. It is applied in the cdmaOne mobile network

Inter-Symbol Interference (ISI) is an interference effect where energy from prior symbols in a bit stream is present in later symbols. ISI is normally caused by filtering of the data streams.

IP Multimedia Services Identity Module (ISIM) is an application running on a Universal Integrated Circuit Card (UICC) smart card in a 3G mobile telephone in the IP Multimedia Subsystem (IMS). It contains parameters for identifying and authenticating the user to the IMS. The ISIM application can co-exist with SIM and USIM on the same UICC making it possible to use the same smart card in both GSM networks and earlier releases of UMTS.

iTAP, also known as T9 TM text input, is a application installed on wireless phones and handheld devices that allows you to type messages with just one key press per letter using the keypad. It is a much easier text input method than the traditional multi-tapping.

International Telecommunications Union (ITU) is a United Nations agency that deals with telecommunications issues.

Interworking Function (IWF) is a technique for interfacing data between a wireless system and the telephone network. It usually involves the use of modems or data terminal adapters to convert the data transmitted over the air interface and mobile network to a format that can be recognized and carried by the public telecommunications network.