Mobile phone card is also called SIM card

SIM card is the abbreviation of (Subscriber Identity Module), also known as smart card, user identity card, which is required for GSM digital mobile phones. This card must be installed before it can be used. It stores digital mobile phone customer information, encrypted keys and other content on a computer chip, which can be used to identify GSM network customers and encrypt customer voice information during calls. The use of SIM cards completely prevents parallel calls and phone calls from being eavesdropped, and the production of SIM cards is strictly in accordance with GSM international standards and specifications, thus reliably ensuring customers' normal communications. The SIM card you get when you first connect to the Internet is a big card, and the small card is embedded in the big card. Currently, mobile phones generally use small cards. You can remove the small card from the big card and use it. SIM cards come in different sizes. The size of a large card is 54mm×85mm (standard credit card size), and the size of a small card is 25mm×15mm (smaller than an ordinary stamp). In fact, the small card is the piece with the chip on the big card. What really works on the "big card" is the "small card" on it. The "small card" can be removed from the big card. At present, the popular style in China is "small card", and the small card can also be replaced by "large card" (just have a card holder). "Large card" and "small card" are respectively suitable for different types of GSM mobile phones. Early models such as Motorola GC87C, 308C and other mobile phones used "large card". Nowadays, new models basically use "big card". "Little Card". The application of SIM card in GSM system separates the card and mobile phone, and the SIM card uniquely identifies a customer. A SIM card can be inserted into any GSM mobile phone for use, and the communication fees incurred by using the mobile phone are recorded on the customer account uniquely identified by the SIM card. SIM card capacities include 8K, 16K, 32K, and 64K, among which large-capacity SIM cards above 16K are collectively called multi-function STK cards.

In order to prevent others from using your SIM card without authorization, the SIM card is set with a personal identification password PIN code. As long as the user has set the PIN code, every time the user turns on the phone, a message will appear on the screen asking for a 4-digit PIN code. , the initial PIN code is 1234 or 0000. If you enter the wrong PIN code three times in a row, the phone will display the words "Enter PUK code" or "Locked", indicating that the SIM card has been locked. Do not press the phone again at this time. Keyboard, because if the PIN unlock code is entered more than 10 times, the SIM card will be automatically discarded. At this time, you need to bring the SIM card ID card to the mobile business hall and the service staff will unlock it for you.

PIN2: Personal identification code 2, which allows users to use certain special functions that require SIM card support, such as setting call billing, passwords, etc., which require network support. Currently, users do not need to use PIN2 code.

Currently, there are three companies issuing SIM cards in China: China Telecom, China Unicom and China Mobile. China Telecom's SIM card is fully launched by China Telecom with the word "China Telecom" and its emblem. China Unicom's SIM cards have a uniform pattern across the country, with scenic spots on the front and unified precautions, the words "China Unicom" and its emblem on the back. China Mobile's SIM cards are designed and issued by each locality. The front of the SIM card is generally printed with the earth, the word "China Mobile" and its emblem, and the reverse side is the name of the local competent authority, local scenic spots, celebrities, zodiac signs, and advertisements. wait. The SIM card is made with A-level encryption method and stores user data, authentication method and key, which can be used by the GSM system to authenticate the user's identity. At the same time, users complete the connection with the system and the exchange of information through it.