ABOUT SIM CARD.pdf

8/10/2019 ABOUT SIM CARD.pdf

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ow a Sim Card work

A subscrib

an integrated circuit that securely

related key used to identify and a

as mobile phones and computers ).

A SIM circuit is embedded into a r

can be transferred between differ

card standards .[1] SIM cards were

0.76 mm). The development of ph

smaller SIM cards where the qua

A SIM card contains its unique se

security authentication and cipheri

a list of the services the user has

number (PIN) for ordinary use an

HistoryThe SIM was initially specified by

specification with the number TS

behavior of the SIM. With the dev

ow a Sim Card work

r identity module or subscriber identification

stores the international mobile subscriber identity

thenticate subscribers on mobile telephony devic

.

emovable plastic card. This plastic card is called

nt mobile devices. A SIM card follows certain sm

first made the same size as a credit card (85.60

ysically smaller mobile devices prompted the dev

tity of card surrounding the integrated circuit is re

ial number ( ICCID ), international mobile subscrib

ing information, temporary information related to t

ccess to and two passwords: a personal identific

a personal unblocking code (PUK) for PIN unloc

the European Telecommunications Standards Ins

1.11. This specification describes the physical a

lopment of UMTS the specification work was par

module (SIM) is

(IMSI) and the

es (such

"SIM card" and

art

m 53.98 mm

elopment of

duced.

er identity (IMSI),

he local network,

tion

king.

titute in the

d logical

tially transferred
http://en.wikipedia.org/wiki/Integrated_circuithttp://en.wikipedia.org/wiki/Integrated_circuithttp://en.wikipedia.org/wiki/Subscriber_identity_modulehttp://en.wikipedia.org/wiki/Mobile_phonehttp://en.wikipedia.org/wiki/Computerhttp://en.wikipedia.org/wiki/Smart_cardhttp://en.wikipedia.org/wiki/Subscriber_identity_modulehttp://en.wikipedia.org/wiki/Subscriber_identity_modulehttp://en.wikipedia.org/wiki/Personal_identification_numberhttp://en.wikipedia.org/wiki/International_mobile_subscriber_identityhttp://en.wikipedia.org/wiki/Telephonyhttp://en.wikipedia.org/wiki/Telephonyhttp://en.wikipedia.org/wiki/Smart_cardhttp://en.wikipedia.org/wiki/ICCIDhttp://en.wikipedia.org/wiki/Personal_identification_numberhttp://en.wikipedia.org/wiki/Personal_unblocking_codehttp://en.wikipedia.org/wiki/European_Telecommunications_Standards_Institutehttp://en.wikipedia.org/wiki/UMTShttp://en.wikipedia.org/wiki/Smart_cardhttp://en.wikipedia.org/wiki/Personal_identification_numberhttp://en.wikipedia.org/wiki/European_Telecommunications_Standards_Institutehttp://en.wikipedia.org/wiki/UMTShttp://en.wikipedia.org/wiki/European_Telecommunications_Standards_Institutehttp://en.wikipedia.org/wiki/Personal_unblocking_codehttp://en.wikipedia.org/wiki/Personal_identification_numberhttp://en.wikipedia.org/wiki/Personal_identification_numberhttp://en.wikipedia.org/wiki/ICCIDhttp://en.wikipedia.org/wiki/Subscriber_identity_modulehttp://en.wikipedia.org/wiki/Smart_cardhttp://en.wikipedia.org/wiki/Smart_cardhttp://en.wikipedia.org/wiki/Computerhttp://en.wikipedia.org/wiki/Mobile_phonehttp://en.wikipedia.org/wiki/Telephonyhttp://en.wikipedia.org/wiki/Subscriber_identity_modulehttp://en.wikipedia.org/wiki/International_mobile_subscriber_identityhttp://en.wikipedia.org/wiki/Integrated_circuit


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to 3GPP . 3GPP is now responsibl

and USIM (TS 31.102) and ETSI f

The first SIM card was made in 1

the first 300 SIM cards to the Finn

Design

SIM chip structure and packaging

There are three operating voltage

and C, respectively). The operatin

V. SIM cards produced subseque

V and 1.8 V.

Modern SIM cards allow applicati

applications communicate with th

initially specified by 3GPP in TS 1

numbering). ETSI and 3GPP mai

102 223, ETSI TS 102 241, ETSI

initially written in native code usin

applications, Java Card was take

specifications of interest are main

DataSIM cards store network-specific i

network. The most important of th

Identity (LAI) and Operator-Specif

data such as the SMSC (Short MService Dialing Numbers (SDN),

applications. (Refer to GSM 11.11

SIM cards can come in various da

of 250 contacts to be stored on th

Codes (MNCs) or "network identifi

e for the further development of applications like

or the further development of the physical card UI

91 by Munich smart-card maker Giesecke & Dev

ish wireless network operator Radiolinja .[2][3]

s for SIM cards: 5 V, 3 V and 1.8 V ( ISO/IEC 781

g voltage of the majority of SIM cards launched b

tly are compatible with 3 V and 5 V. Modern car

ns to be loaded when the SIM is in use by the su

handset or a server using SIM application toolkit

1.14 (there is an identical ETSI specification with

tain the SIM specifications; the main specificatio

S 102 588, and ETSI TS 131 111. SIM toolkit a

proprietary APIs. In order to allow interoperabilit

as the solution of choice by ETSI [ Additional stan

ained by Global Platform.

nformation used to authenticate and identify subs

ese are the ICCID, IMSI, Authentication Key ( Ki),

ic Emergency Number. The SIM also stores othe

ssage Service Center) number, Service Providerdvice-Of-Charge parameters and Value Added

.)

ta capacities, from 32 KB to at least 128 KB. All

e SIM, but while the 32 KB has room for 33 Mobile

iers", the 64 KB version has room for 80 MNCs. T

IM (TS 51.011)

ICC .

rient , who sold

-3 classes A, B

efore 1998 was 5

s support 5 V, 3

bscriber. These

, which was

different

s are: ETSI TS

plications were

y of the

dards and

cribers on the

Local Area

carrier-specific

Name (SPN),ervice (VAS)

llow a maximum

Network

his is used by
http://en.wikipedia.org/wiki/3GPPhttp://en.wikipedia.org/wiki/Java_Cardhttp://en.wikipedia.org/wiki/Mobile_Network_Codehttp://en.wikipedia.org/wiki/UICChttp://en.wikipedia.org/wiki/Giesecke_%26_Devrienthttp://en.wikipedia.org/wiki/Radiolinjahttp://en.wikipedia.org/wiki/Radiolinjahttp://en.wikipedia.org/wiki/Subscriber_identity_modulehttp://en.wikipedia.org/wiki/Subscriber_identity_modulehttp://en.wikipedia.org/wiki/ISO/IEC_7816http://en.wikipedia.org/wiki/Subscriber_identity_modulehttp://en.wikipedia.org/wiki/Mobile_Network_Codehttp://en.wikipedia.org/wiki/UICChttp://en.wikipedia.org/wiki/Giesecke_%26_Devrienthttp://en.wikipedia.org/wiki/Mobile_Network_Codehttp://en.wikipedia.org/wiki/Mobile_Network_Codehttp://en.wikipedia.org/wiki/Mobile_Network_Codehttp://en.wikipedia.org/wiki/Subscriber_identity_modulehttp://en.wikipedia.org/wiki/Java_Cardhttp://en.wikipedia.org/wiki/ISO/IEC_7816http://en.wikipedia.org/wiki/File:Smartcard_chip_structure_and_packaging_EN.svghttp://en.wikipedia.org/wiki/Subscriber_identity_modulehttp://en.wikipedia.org/wiki/Subscriber_identity_modulehttp://en.wikipedia.org/wiki/Radiolinjahttp://en.wikipedia.org/wiki/Giesecke_%26_Devrienthttp://en.wikipedia.org/wiki/UICChttp://en.wikipedia.org/wiki/3GPP


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network operators to store information on preferred networks, mostly used when the SIM is not in its

home network but is roaming . The network operator that issued the SIM card can use this to have a

phone connect to a preferred network, in order to make use of the best price and/or quality network

instead of having to pay the network operator that the phone 'saw' first. This does not mean that a

phone containing this SIM card can connect to a maximum of only 33 or 80 networks, but it meansthat the SIM card issuer can specify only up to that number of preferred networks; if a SIM is outside

these preferred networks it will use the first or best available network.

ICCID

Each SIM is internationally identified by its integrated circuit card identifier (ICCID). ICCIDs are

stored in the SIM cards and are also engraved or printed on the SIM card body during a process

called personalization. The ICCID is defined by the ITU-T recommendation E.118 as the Primary

Account Number . Its layout is based on ISO/IEC 7812 . According to E.118, the number is up to 22

digits long, including a single check digit calculated using the Luhn algorithm . However, the GSM

Phase 1 defined the ICCID length as 10 octets (20 digits) with operator-specific structure.

The number is composed of the following subparts:

Issuer identification number (IIN)

Maximum of seven digits:

Major industry identifier (MII), 2 fixed digits, 89 for telecommunication purposes.

Country code , 13 digits, as defined by ITU-T recommendation E.164 .

Issuer identifier, 14 digits.

Individual account identification

Individual account identification number. Its length is variable, but every number under one IIN

will have the same length.

Check digit

Single digit calculated from the other digits using the Luhn algorithm .

With the GSM Phase 1 specification using 10 octets into which ICCID is stored as packed BCD, the

data field has room for 20 digits with hexadecimal digit "F" being used as filler when necessary.

In practice, this means that on GSM SIM cards there are 20-digit (19+1) and 19-digit (18+1) ICCIDs

in use, depending upon the issuer. However, a single issuer always uses the same size for its

ICCIDs.
http://en.wikipedia.org/wiki/Roaminghttp://en.wikipedia.org/wiki/ISO/IEC_7812http://en.wikipedia.org/wiki/Luhn_algorithmhttp://en.wikipedia.org/wiki/List_of_country_calling_codeshttp://en.wikipedia.org/wiki/ITU-Thttp://en.wikipedia.org/wiki/ITU-Thttp://en.wikipedia.org/wiki/E.164http://en.wikipedia.org/wiki/Luhn_algorithmhttp://en.wikipedia.org/wiki/Octet_(computing)http://en.wikipedia.org/wiki/Octet_(computing)http://en.wikipedia.org/wiki/Luhn_algorithmhttp://en.wikipedia.org/wiki/E.164http://en.wikipedia.org/wiki/ITU-Thttp://en.wikipedia.org/wiki/List_of_country_calling_codeshttp://en.wikipedia.org/wiki/Luhn_algorithmhttp://en.wikipedia.org/wiki/ISO/IEC_7812http://en.wikipedia.org/wiki/Roaming


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To confuse matters more, SIM factories seem to have varying ways of delivering electronic copies of

SIM personalization datasets. Some datasets are without the ICCID checksum digit, others are with

the digit.

As required by E.118, The ITU regularly publishes a list of all internationally assigned IIN codes in its

Operational Bulletins. The most recent list, as of November 2013, is in Operational Bulletin No. 1040 .

International mobile subscriber identity (IMSI)

SIM cards are identified on their individual operator networks by a unique International Mobile

Subscriber Identity (IMSI). Mobile network operators connect mobile phone calls and communicate

with their market SIM cards using their IMSIs. The format is:

The first three digits represent the Mobile Country Code (MCC).

The next two or three digits represent the Mobile Network Code (MNC). Three-digit MNC codes

are allowed by E.212 but are mainly used in the United States and Canada. The next digits represent the Mobile Subscriber Identification Number ( MSIN ). Normally there

will be 10 digits but would be fewer in the case of a 3-digit MNC or if national regulations indicate

that the total length of the IMSI should be less than 15 digits.

Digits are different from country to country.

Authentication key (K i)

The Kn i is a 128-bit value used in authenticating the SIMs on the mobile network. Each SIM holds a

unique K i assigned to it by the operator during the personalization process. The K i is also stored in a

database (termed authentication center or AuC) on the carrier's network.

The SIM card is designed not to allow the K i to be obtained using the smart-card interface . Instead,

the SIM card provides a function, Run GSM Algorithm , that allows the phone to pass data to the SIM

card to be signed with the K i. This, by design, makes usage of the SIM card mandatory unless the

Ki can be extracted from the SIM card, or the carrier is willing to reveal the K i. In practice, the GSM

cryptographic algorithm for computing SRES_2 (see step 4, below) from the K i has certain

vulnerabilities [6] that can allow the extraction of the K i from a SIM card and the making of a duplicate

SIM card .

Authentication process:

1. When the Mobile Equipment starts up, it obtains the International Mobile Subscriber Identity

(IMSI) from the SIM card, and passes this to the mobile operator requesting access and

authentication. The Mobile Equipment may have to pass a PIN to the SIM card before the

SIM card will reveal this information.

2. The operator network searches its database for the incoming IMSI and its associated K i.
http://www.itu.int/pub/T-SP-OB.1040-2013http://en.wikipedia.org/wiki/International_Mobile_Subscriber_Identityhttp://en.wikipedia.org/wiki/International_Mobile_Subscriber_Identityhttp://en.wikipedia.org/wiki/Mobile_network_operatorhttp://en.wikipedia.org/wiki/Mobile_network_operatorhttp://en.wikipedia.org/wiki/Mobile_Country_Codehttp://en.wikipedia.org/wiki/Mobile_Country_Codehttp://en.wikipedia.org/wiki/Mobile_Network_Codehttp://en.wikipedia.org/wiki/MSINhttp://en.wikipedia.org/wiki/Network_switching_subsystemhttp://en.wikipedia.org/wiki/(U)SIM_Interfacehttp://en.wikipedia.org/wiki/Subscriber_identity_modulehttp://en.wikipedia.org/wiki/SIM_cloninghttp://en.wikipedia.org/wiki/SIM_cloninghttp://en.wikipedia.org/wiki/SIM_cloninghttp://en.wikipedia.org/wiki/SIM_cloninghttp://en.wikipedia.org/wiki/Subscriber_identity_modulehttp://en.wikipedia.org/wiki/(U)SIM_Interfacehttp://en.wikipedia.org/wiki/Network_switching_subsystemhttp://en.wikipedia.org/wiki/MSINhttp://en.wikipedia.org/wiki/Mobile_Network_Codehttp://en.wikipedia.org/wiki/Mobile_Country_Codehttp://en.wikipedia.org/wiki/Mobile_network_operatorhttp://en.wikipedia.org/wiki/International_Mobile_Subscriber_Identityhttp://en.wikipedia.org/wiki/International_Mobile_Subscriber_Identityhttp://www.itu.int/pub/T-SP-OB.1040-2013


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3. The operator network the

signs it with the K i associ

number known as Signed


SIM card. The SIM card sEquipment along with en

operator network.


the Mobile Equipment ret

Mobile Equipment is gran

further communications b

Location area identity (L

The SIM stores network state info

Operator networks are divided int

SIM and sends it back to the oper

will take data off the SIM, and sea

generates a Random Number (RAND, which is

ted with the IMSI (and stored on the SIM card), c

Response 1 (SRES_1).

sends the RAND to the Mobile Equipment, whic

igns it with its K i, producing SRES_2, which it givryption key K c. The Mobile Equipment passes SR

compares its computed SRES_1 with the compu

rned. If the two numbers match, the SIM is auth

ted access to the operator's network. K c is used t

etween the Mobile Equipment and the network.

AI)

rmation, which is received from the Location Area

Location Areas, each having a unique LAI num

When the device changes locations, it stores the

ator network with its new location. If the device is

rch for the prior LAI.

nonce ) and

omputing another

passes it to the

s to the MobileES_2 on to the

ted SRES_2 that

nticated and the

encrypt all

Identity (LAI).

er.

new LAI to the

power cycled, it
http://en.wikipedia.org/wiki/Location_Area_Identityhttp://en.wikipedia.org/wiki/Cryptographic_noncehttp://en.wikipedia.org/wiki/Location_Area_Identityhttp://en.wikipedia.org/wiki/Location_Area_Identityhttp://en.wikipedia.org/wiki/Cryptographic_nonce


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SMS messages and co

of SMS messages and phone boo

pairs: entries containing multiple

stored on the SIM card. When a u

break them up into multiple entrie

number of contacts and message

five messages and 20 contacts w

Formats [edit ]

Full-size SIM (1FF), mini-SIM (2FF), mi

tacts

Most SIM cards will orthogonally

k contacts. The contacts are stored in simple "na

hone numbers and additional phone numbers wil

ser tries to copy such entries to a SIM the hands

, discarding any information that is not a phone n

stored depends on the SIM; early models would

ile modern SIM cards can usually store over 250

cro-SIM (3FF) and nano-SIM (4FF)

store a number

e and number"

l usually not be

t's software will

umber. The

store as few as

contacts
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Micro-SIM (from bottom) with mini-SIM and full SIM brackets from Telia in Sweden

The memory film from a micro SIM card without the plastic backing plate, next to a US dime , which is approx. 18 mm

in diameter.

Embedded SIM from M2M supplier Eseye with an adapter board for evaluation in a Mini-SIM socket

SIM cards have been made smaller over the years; functionality is independent of format. Full-size

SIMs were followed by mini-SIMs, micro-SIMs, and nano-SIMs. SIMs are also made to be

embedded in devices.

SIM card sizes

SIM card Introduced Standard referenceLength

(mm)

Width

(mm)

Thickness

(mm)

Volume

(mm 3)
http://en.wikipedia.org/wiki/Dime_(United_States_coin)http://en.wikipedia.org/wiki/Dime_(United_States_coin)http://en.wikipedia.org/wiki/Dime_(United_States_coin)http://en.wikipedia.org/wiki/File:Disassembled_SIM_Card_Film.JPGhttp://en.wikipedia.org/wiki/File:Telia_micro_SIM_with_brackets.jpg


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Full-size

(1FF)1991

ISO/I

1

Mini-SIM

(2FF)circa 1996

ISO/I

000

Micro-SIM

(3FF)2003

ETSI

V9.0.

Nano-SIM

(4FF)early 2012

ETSI

V11.0.

Embedded-

SIM

JEDE

4.8, S

Full-size SIM

The full-size SIM

the size of a credit card (85.60 m

Mini-SIM

The mini-SIM (or 2FF) card has th

normally supplied within a full-siz

arrangement (defined in ISO/IECrequiring a full-size card, or in a d

C 7810 :2003, ID-85.60 53.98

C 7810:2003, ID-25.00 15.00

S 102 221

, Mini-UICC15.00 12.00

S 102 221

.012.30 8.80

Design Guide

N-86.00 5.00

(or 1FF, 1st form factor) was the first form factor t

53.98 mm 0.76 mm).

e same contact arrangement as the full-size SIM

card carrier, attached by a number of linking pie

7810 as ID-1/000 ) allows such a card to be used ivice requiring a mini-SIM card after breaking the

0.76 3511.72

0.76 285.00

0.76 136.80

0.67 72.52


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the previous format to the contact area while maintaining the existing contact arrangements. A

small rim of isolating material is left around the contact area to avoid short circuits with the

socket. The 0.67 mm thickness of the NANOSIM is about 12% less than the 0.76 mm of its

predecessor. 4FF can be put into adapters for use with devices taking 2FF or 3FF

SIMs. The iPhone 5 , released in September 2012, was the first device to use a nano-SIM card.Embedded-SIM / Embedded Universal Integrated Circuit Card(eUICC)

SIMs for M2M applications are available in a surface mount SON-8

package which may be soldered directly onto a circuit board.

The surface mount format provides the same electrical interface as the full size, 2FF and 3FF

SIM cards, but is soldered to the circuit board as part of the manufacturing process.

In M2M applications where there is no requirement to change the SIM card, this avoids the

requirement for a connector, improving reliability and security. GSMA has been discussing thepossibilities of a software based SIM card since 2010. [14] While Motorola noted that eUICC is

geared at industrial devices, Apple "disagreed that there is any statement forbidding the use of

an embedded UICC in a consumer product." in 2012, [15] The European Commission has selected

the Embedded UICC format for its in-vehicle emergency call service know as eCall . All new car

models in the EU will need to have one by 2015 to instantly connect the car to the emergency

services in case of an accident. In Russia there is a similar plan with the ERA GLONASS

regional satellite positioning system and in Brazil with the SIMRAV anti-theft system. [16]

SecurityIn July 2013, it was revealed that Karsten Nohl, a cryptographer and

security researcher from SR Labs had discovered vulnerabilities in some SIM cards that enabled

them to be hacked to provide root access . The cards affected use the Data Encryption

Standard (DES) which, despite its age, is still used by some operators. [19] Cards using the more

recent Advanced Encryption Standard (AES) or Triple DES standards are not affected. [19] Among

other risks, the hack could lead to the phone being remotely cloned or allow payment credentials

from the SIM to be stolen. [19] Further details of the research were to be given at BlackHat on July

31, 2013.

In response, the International Telecommunication Union said that the development was "hugely

significant" and that it would be contacting its members.

DevelopmentsWhen GSM was already in use, the specifications were further developed and enhanced with

functionality l ike SMS , GPRS , etc. These development steps are referred as releases by ETSI.


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Within these development cycles, the SIM specification was enhanced as well: new voltage

classes, formats and files were introduced. In GSM-only times, the SIM consisted of the

hardware and the software. With the advent of UMTS this naming was split: the SIM was now an

application and hence only software. The hardware part was called UICC. This split was

necessary because UMTS introduced a new application, the Universal Subscriber IdentityModule (USIM). The USIM brought, among other things, security improvements like the mutual

authentication and longer encryption keys and an improved address book.

"SIM cards" in developed countries are today usually UICCs containing at least a SIM and a

USIM application. This configuration is necessary because older GSM only handsets are solely

compatible with the SIM [application] and some UMTS security enhancements do rely on the

USIM [application].

The equivalent of SIM on CDMA networks is the R-UIM (and the equivalent of USIM is CSIM ).

A virtual SIM is a mobile phone number provided by a mobile network operator that does notrequire a SIM card to connect phone calls to a user's mobile phone.

Usage in mobile phone standardsThe use of SIM cards is mandatory in GSM devices.

The satellite

phone networks Iridium , Thuraya and Inmarsat 's BGAN also use SIM cards. Sometimes, these

SIM cards work in regular GSM phones and also allow GSM customers to roam in satellite

networks by using their own SIM card in a satellite phone.

Japan's 2G PDC system (which was shut down in 2012; SoftBank Mobile has already shut down

PDC from March 31, 2010) also specifies a SIM, but this has never been implemented

commercially. The specification of the interface between the Mobile Equipment and the SIM is

given in the RCR STD-27 annex 4. The Subscriber Identity Module Expert Group was a

committee of specialists assembled by the European Telecommunications Standards Institute

(ETSI) to draw up the specifications ( GSM 11.11) for interfacing between smart cards and

mobile telephones. In 1994, the name SIMEG was changed to SMG9.

Japan's current and next generation cellular systems are based on W-CDMA

(UMTS) and CDMA2000 and all use SIM cards. However, Japanese CDMA2000-based phonesare locked to the R-UIM they are associated with and thus, the cards are not interchangeable

with other Japanese CDMA2000 handsets (though they may be inserted into GSM/WCDMA

handsets for roaming purposes outside Japan).

CDMA -based devices originally did not use a removable card, and the service for these phones

bound to a unique identifier contained in the handset itself. This is most prevalent in operators in


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the Americas. The first publication of the TIA-820 standard (also known as 3GPP2 C.S0023) in

2000 defined the Removable User Identity Module ( R-UIM). Card-based CDMA devices are

most prevalent in Asia.

The equivalent of a SIM in UMTS is called the Universal Integrated Circuit Card ( UICC ), which

runs a USIM application. The UICC is still colloquially called a SIM card

SIM and carriersThe SIM card introduced a new and significant business opportunity for MVNOs mobile virtual

network operators who lease capacity from one of the network operators rather than owning

or operating a cellular telecoms network, and only provide a SIM card to their customers.

MVNOs first appeared in Denmark, Hong Kong, Finland and the UK. Today they exist in over 50

countries, including most of Europe, United States, Canada, Mexico, Australia and parts of Asia,

and account for approximately 10% of all mobile phone subscribers around the world.

On some networks, the mobile phone is locked to its carrier SIM card , meaning that the phone

only works with SIM cards from the specific carrier. This is more common in markets where

mobile phones are heavily subsidized by the carriers, and the business model depends on the

customer staying with the service provider for a minimum term (typically 12 or 24 months). SIM

cards that are issued by providers with an associated contract are called Sim only deals.

Common examples are the GSM networks in the United States, Canada, Australia, the UK and

Poland. Many businesses offer the ability to remove the SIM lock from a phone, effectively

making it possible to then use the phone on any network by inserting a different SIM card.

Mostly, GSM and 3G mobile handsets can easily be unlocked and used on any suitable networkwith any SIM card.

In countries where the phones are not subsidised, e.g. , India, Israel and Belgium, all phones are

unlocked. Where the phone is not locked to its SIM card, the users can easily switch networks

by simply replacing the SIM card of one network with that of another while using only one phone.

This is typical, for example, among users who may want to optimise their carrier's traffic by

different tariffs to different friends on different networks, or when traveling internationally

Documents

ABOUT SIM CARD.pdf