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- Subscriber Identity Module (SIM)
A SIM card is about the size of a U.S. Dime
- A subscriber identity module (a SIM Card) is a
smart card which securely stores the key identifying a mobile phone service subscriber, as well as subscription
information, preferences and text messages. The equivalent of a SIM in UMTS is a Universal Subscriber Identity
Module (USIM).
The SIM stores network state information such as its current location area identity (LAI). If the handset is turned
off and back on again it will take data off the SIM and search for the LAI it was in.
This saves time by avoiding having to search the whole list of frequencies that the telephone normally would. Each
SIM is uniquely identified by its ICCID [International Circuit Card ID].
SIM cards identify users uniquely by holding an IMSI.
 The
SIM - Subscriber Identity Module - is a smart chip card, about the size of a postage stamp. A SIM card from a UK mobile phone on the Orange network. The card was originally punched
out of a Credit Card sized sheet of plastic. The distinctive shape fits inside a socket within any GSM mobile phone.
Photo by Salim Fadhley
- International Mobile Subscriber
Identity (IMSI)
IMSI[im-zee] is an acronym for International
Mobile Subscriber Identity. This is a unique number that is associated with all GSM and UMTS network mobile phone
users.
The number is stored in the SIM. It is sent by the mobile to the network and is used to look up the other details
of the mobile in the HLR or as locally copied in the VLR. In order to avoid the subscriber being identified and
tracked by eavesdroppers on the radio interface, the IMSI is sent as rarely as possible and a randomly generated
TMSI is sent instead.
An IMSI is usually fifteen digits long. However, they can be shorter (eg. MTN SouthAfrica's are 14 digits).
The first three digits are the country code (MCC), and the next digits are the network code (MNC). The MNC can
be either two digits long (normal e.g. in Europe) or three digits long (normal in North America), the remaining
digits, up to the maximum length are the unique subscriber number (MSIN) within the network's customer base.
- Change your SIM Card - Change
your Mobile Number
The SIM card contains a microprocessor chip, which stores unique information about your account, including your
phone number and identifies you to the network.
So it is NOT your cell phone which determines your telephone number, but it is your SIM card.
Instead, subscribers activate their phones by inserting SIM cards. Therefore, every time you change your SIM card,
you are getting a new telephone number.
A SIM card is actually a tiny computer in your phone.
Current SIMs typically have 16 to 64 kb of memory, which provides plenty of room for storing hundreds of personal
phone numbers, text messages, value-added services and important for us: position data (coordinates) of tracked
animals.
- SIM Card Stores your Phone
Number, it's the size of a postage stamp
 The
embedded circuitry located on the SIM card stores information about the services that are available to you as a
local subscriber.
The SIM card, provided by a local GSM cell phone operator, snaps into the back of a GSM cell phone to make you
a local subscriber.
From
Wikipedia, the free encyclopedia
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