International Mobile Subscriber Identity Number which uniquely identifies a subscriber in the GSM-PLMN.
Interim Standard
Interim Standard-41.  A mobile communication standard that defines how service providers use signaling between cellular switches and other network devices for intersystem handover/hand-off and automatic roaming.  The IS-41 messaging language allows the exchange of information between different brands of equipment on  an SS7 or x.25 network.
Interim Standard 53.  A high-level recommendation of uniform services and features Including preferred language, conference calling, remote call features, message waiting indication, call delivery short message point-to-point delivery , calling number id, call transfer, mobile access hunting, 3-way calling, password call acceptance, subscriber PIN access.
Interim Standard 54.  Standard for the air interface between cellular phones and a cell site using analog control channel.
Interim Standard 136.  Standard for the air interface between cellular phones and cell site using a digital control channel.
Integrated Services Digital Network.  A network architecture that includes end-to-end digital connections and PSTN analog loop connections.  It integrates the following communications services onto one 64 kb/s (kilobytes per second) digital channel, digital voice, high-speed data, telex, telemetry, facsimile, and slow-scan video.
International Organization for Standardization.  Worldwide federation to promote the development of standardization and related activities in the world with a view to facilitating the international exchange of goods and services, and to developing cooperation in the areas of intellectual, scientific, technical and economic activity.
International Telegraph Union.  Founded in 1837 in the US regulated telegraph.  Became International Telecommunication Union.
A telecommunications service that meets market demand through the implementation of different advanced services for network operators and service providers within the existing telephony network.