The Full Meaning of SIM and Its Functions

What’s the full meaning of SIM card and its functions? Why is it the most important part of your device? Since technology is advancing, everybody uses the SIM card but is not everyone that still know the meaning and how it functions in a phone.

Firstly, lets define the SIM – is an integrated circuit specially created for storing the international mobile subscriber identity – IMSI, and is used to identify the holder of a mobile device. SIM cards are used on various devices like mobile or satellite phones, cameras, computers, etc.

The SIM card cannot work without a universal integrated circuit card or just UICC. The first UICC physical smart cards were the size of a bank card; they have changed and become way smaller over time. Presently, every SIM card contains the following information on it:

  • ICCID – integrated circuit card identifier;
  • IMSI – international mobile subscriber identity;
  • Ciphering information;
  • Security authentication;
  • Local network information;
  • List of services for a user;
  • Personal identification number;
  • Personal unblocking code.  

The design of the SIM card has also been changed since its creation. There are currently three different operating voltages of SIM card:

  • 5V;
  • 3V;
  • 1.8V.  

Majority of SIM cards had an operating voltage of 5V as at 1998 but as at today, the modern cards can support any voltage. All SIM cards allow applications to load even if a subscriber is using the SIM; this is made possible with the SIM application toolkit which is initially specified by 3GPP. The toolkit application helps the SIM to hold its specialization. The SIM toolkit application was written in a native code using the proprietary APIs.

SIM Formats

SIM cards have been made smaller over the years. The full-sized formats could be either mini or nano.

Full-Size SIM

The first full-size SIM was in size of a standard credit card. It was a big challenge for the first mobile users to maintain this SIM card. Eventually, it was changed to much smaller SIM cards.


The Mini SIM was supplied with a full-size card carrier. This trick was made enable the use of Mini SIMs in devices made to work with full SIM cards.

Micro SIM

The next generation of SIM cards had the same thickness as the previous one, but it was reduced in length and width. It is now the most used SIM card all over the world. It was first introduced by the European Telecommunications Standards Institute. The size of the card was chosen to fit the devices that can`t work with any other card. The micro-SIM was also designed for the backward compatibility which was a major issue with Mini SIM.

SIM Card Nano  

This type of SIM card was introduced in October 2012, after which various mobile telecommunication companies started to make devices compatible with it. The Nano SIM are really small. The first mobile phone that could use a Nano SIM card was the iPhone 5.

Multi-SIM Devices

It is possible to use several SIM cards with one device. Developing countries are the biggest markets for the multiple SIM cards devices. Nevertheless, the competition is the source of progress!

International SIM card

As it was mentioned earlier, every SIM card is identified by the International Mobile Subscriber Identity or IMSI. Mobile operators use this information to communicate with each other. It is a very simple code that is used internationally! The format of every mobile phone number consists of these characteristics:

The mobile country code always makes up the first three digits of every mobile number; The following two digits represent Mobile Network Code; however, it can also be a three-digit code in the USA and Canada.

The resulting digits are the mobile subscriber identification number or MSIN. It is usually a 10 digits number, but some countries allow up to 15 digits. 
Data in SIM

Most SIM cards store SMS data and phone book contacts. It usually stores the numbers in simple pairs – name and number. The SIM cards can usually store up to 250 numbers and it is not possible to store several numbers for one contact in a SIM, usually it breaks them into several contacts with the same name.

Every SIM card gathers and stores network specific information to identify a subscriber. The most important information gathered are:

  • Operator Specific Emergency Number;
  • Local Area Identity;
  • Authentication Key;
  • IMSI;
  • ICCID.

Nevertheless, every SIM card also carries information, like:

  • Value Added Service;
  • Advice of Charge parameters;
  • Service Dialing Number;
  • Service Provider Name;
  • Short Message Service Center.  

SIM cards come in various data capacities. The minimum data storage for a SIM card is 8 KB while the maximum can be up to 256 KB, which is more than enough room for 250 contacts.


  1. in addition to this post,here are the drawbacks of a SIM card?SIM cards are fairly simple. They have practically no function without an accompanying smartphone and are increasingly reliant on third-party apps to address functionality, such asconnecting to multiple networks or using more than one phone number.And because they are simple pieces of plastic, their benefit is largely subject to the will of the carrier. If youbuy a phone that is locked to one carrier, putting a different carrier's SIM requires an unlock code, which isoften expensive to obtain and confusing to enter. Typically the SIM lock is in exchange for a subsidized phone (so you can't buy a cheap phone on one carrier then switch over an use another before you've paid back the subsidy over the life of your contract).These days, Apple sells the iPhone SIM-unlocked in most countries, including the U.S., Canada and the U.K. While customers have to pay more upfront for an unlocked version of the iPhone, they can use the phonewith any compatible SIM card, as long as the phone works with that carrier's network. The latest iPhone, the 6s, supports 23 LTE bands, which comprises most of the world's carriers. What is Apple SIM?In 2014, alongside the iPad Air 2 and iPad mini 4, Apple unveiled Apple SIM, a way for the company to offer dynamic network choice to its customers without the hassle of getting SIMs from multiple carriers. Apple SIM allows iPad owners to connect to compatible networks in over 180 countries; in the U.S., those carriers include AT&T, Sprint, and T-Mobile. Though the Apple SIM is manufactured by Apple, you still purchase plans from a specific carrier using your credit card — there's no iTunes billing option .You can see Apple's full list on its website. The beauty of Apple SIM is its ability to interface with multiple networks: If your local providers support it, you can swap between network plans depending on which one makes the most sense for your needs; for example, you can swap between Sprint and T-Mobile if you go from a Sprint-heavy part of the country to someplace where T-Mobile's network reigns. When traveling internationally,you can also use Apple partners Gig Sky, Always Online Wireless, andauto purchase per-day or per-megabyte bundles to save on roaming costs.

  2. A SIM card, also known as a subscriber identity module, is a smart cardthat stores data for GSM cellular telephonesubscribers. Such data includes user identity, location and phone number, network authorization data, personal security keys, contact lists and stored text messages. Security features include authenticationand encryptionto protect data and prevent eavesdropping.

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