The full-size SIM card (or 1FF, 1st form factor) was the first form factor to appear. It was the size of a credit card (85.60 mm × 53.98 mm × 0.76 mm). Later, smaller SIM cards are often delivered integrated into a full-size card from where they can be removed. The “SIM card only”, which is usually sold as a product by mobile phone companies, refers to a type of legally binding contract between a mobile operator and a customer. The contract itself takes the form of a credit agreement and is subject to a credit check. The SIM card stores network status information received by the Location Area Identity (LAI). Operator networks are divided into site areas, each with a unique LAI number. When the device changes location, it stores the new LAI on the SIM card and sends it back to the carrier`s network with its new slot. When the device is turned off, it takes the data from the SIM card and looks for the previous LAI. Most SIM cards store a series of SMS messages and phone book contacts. It stores contacts in simple “name and number” pairs. Entries that contain multiple phone numbers and additional phone numbers are usually not stored on the SIM card. When a user tries to copy such entries to a SIM card, the handset`s software divides them into several entries and rejects information that is not a phone number.
The number of contacts and messages stored depends on the SIM card. Early models only stored five messages and 20 contacts, while modern SIM cards can usually store more than 250 contacts.  We hope you have understood the full form and meaning of the SIM card and the functions of the SIM card. About us At Swiflearn, we have one motto: learning must never stop. With over 50500 happy and satisfied students shaping their future among over 590 active teachers, and with over 117431 classes in total, we have come a long way. The founders and core team members of Swiflearn are graduates of IIT Bombay and IIM Ahmedabad, who have secured leading positions in IIT-JEE, NTSE Fellows and the National Olympics. We believe that the personal attention of teachers and academic mentors is very important for the maximum learning of each student, and that is why we focus all our efforts to ensure that each student receives the best possible personalized learning experience from the best teachers in India. Our team has worked in world-class consulting, education and technology companies in the past and is equipped with the best experience in the industry to sincerely strive for every student`s learning with cutting-edge technology. We strive more than anyone else to offer the best quality of learning at the lowest possible cost. A SIM card contains a unique serial number (ICCID), an IMSI (International Mobile Subscriber Identity) number, authentication and security encryption information, temporary information on the local network, a list of services to which the user has access and two passwords: a personal identification number (PIN) for normal use and a personal unlock key (PUK) for unlocking the PIN code. In Europe, the serial SIM number (SSN) is also sometimes accompanied by an international item number (IAN) or a European item number (EAN), which is required when registering online to subscribe to a prepaid card.
The mini SIM card (or 2FF) has the same contact layout as the full-size SIM card and usually comes in a full-size card holder connected by a series of connectors. This arrangement (defined in ISO/IEC 7810 as ID-1/000) allows such a card to be used in a device that requires a full-size card – or in a device that requires a mini SIM card after the connectors break. Since the full-size SIM card is no longer used, some providers refer to the mini SIM as a “standard SIM card” or “normal SIM card”. CDMA phones usually do not use SIM cards. Instead, all the information is stored in the handset itself. This may be less convenient for users because the user cannot change service providers for the same handset. In 2014, Equitel, an MVNO operated by a Kenyan stock bank, announced plans to start issuing lightweight SIM cards to its customers, raising security concerns from the competition, particularly when it comes to the security of mobile money accounts. However, after months of security testing and legal hearings before the country`s Parliamentary Energy, Information and Communications Committee, the Communications Authority of Kenya (CAK) has given the bank the green light to launch its thin SIM cards.  MicroSIM was introduced by the European Telecommunications Standards Institute (ETSI) in collaboration with SCP, 3GPP (UTRAN/GERAN), 3GPP2 (CDMA2000), ARIB, GSM Association (GSMA SCaG and GSMNA), GlobalPlatform, Liberty Alliance and Open Mobile Alliance (OMA) to be installed in devices too small for a mini SIM card.   SIM cards store network-specific information that is used to authenticate and identify participants on the network.
The most important of these are ICCID, IMSI, authentication key (Ki), local area identity (LAI) and operator-specific emergency number. The SIM card also stores other carrier-specific data, such as Short Message Service Center (SMSC) number, service provider name (SPN), service number numbers (SDN), charge notification settings, and value-added service applications (VAS). (See GSM 11.11. ) When GSM was already in use, the specifications were developed and extended with functions such as SMS and GPRS. These stages of development are called by ETSI discharges. During these development cycles, the SIM specification was also improved: new voltage classes, formats and files were introduced. The form factor was mentioned in the UMTS 3GPP SMG9 working group of December 1998, which is the standard-setting body for GSM SIM cards, and the form factor was agreed at the end of 2003.  Modern SIM cards allow applications to be loaded when the SIM card is used by the subscriber. These applications communicate with the handset or a server via the SIM Application Tools KIT originally specified by 3GPP in TS 11.14. (There is an identical ETSI specification with different numbering.) ETSI and 3GPP maintain the SIM specifications. The main specifications are: ETSI TS 102 223 (the toolkit for smart cards), ETSI TS 102 241 (API), ETSI TS 102 588 (application call) and ETSI TS 131 111 (toolbox for more SIM likes). SIM toolbox applications were originally written in native code using proprietary APIs.
To ensure the interoperability of applications, ETSI chose Java Card.  A cross-company collaboration called GlobalPlatform defines certain extensions on the cards, adding additional APIs and features such as greater cryptographic security and the use of contactless RFID.  A SIM card also contains its unique serial number (ICCID), international mobile subscriber identity (IMSI), security information, encryption information, temporary information on the local network, etc. The SIM card contains the necessary information about your network and also contains some of your personal data. SIM cards are identified in their networks of individual operators by a unique International Mobile Subscriber Identity (IMSI). Mobile operators connect mobile phone calls and communicate with their market SIM cards via their IMSIs. The format is: The nano SIM card (or 4FF) was introduced on October 11, 2012, when operators in various countries began rolling it out to phones that supported the format. The Nano-SIM measures 12.3 mm × 8.8 mm × 0.67 mm (0.484 in × 0.346 × 0.026 inch) and reduces the previous size to the contact surface while retaining existing contact agreements. A small edge of insulating material remains around the contact surface to avoid short circuits with the socket. The Nano-SIM is 0.67 mm (0.026 inch) thick, compared to 0.76 mm (0.030 inch) of its predecessors. 4FF may be used in adapters intended for use with devices designed for 2FF or 3FF SIM cards and will be thinned for this purpose, and telephone companies give due notice in this regard.
 An integrated SIM card (eSIM) is a form of programmable SIM card integrated directly into a device. The surface-mountable format provides the same electrical interface as the full-size 2FF and 3FF SIM cards, but is soldered to a printed circuit board as part of the manufacturing process. .