How to choose a mobile phone card for iphone SMS?

This means that if you happen to have two mobile phone cards, you can directly choose these two. Here are some irrelevant ones from Baidu Encyclopedia! ! !

SIM card is the subscriber identification card of digital cellular mobile phone, and its full name is "subscriber identification module". In GSM digital mobile phone system, SIM card plays an extremely important role. It is not only an important part of mobile phone, but also the ID card of every GSM mobile phone user. Therefore, the SIM card realizes the idea that people do not recognize machines [3].

Mobile phone and SIM card together constitute mobile communication terminal equipment. No matter in GSM system or CDMA system, users of digital mobile phones will get a SIM card when they "access the network". SIM card is also called smart card or subscriber identification card, and digital mobile phone can only be used after installation. SIM card is a kind of card with large-scale integrated circuit, which stores the information of digital mobile phone customers, encryption keys and other contents. The network can use it to identify customers and encrypt voice information when customers talk. The use of SIM card completely prevents parallel lines and telephones from being eavesdropped, and the production of SIM card is carried out in strict accordance with international standards and norms, ensuring the normal communication of customers. There is no SIM card installed, so you can only dial emergency numbers such as 1 19, 1 12. The application of SIM card in the system separates the card from the mobile phone, and a SIM card uniquely identifies a customer. The SIM card can be inserted into any mobile phone for use, and the communication expenses generated by using the mobile phone are automatically recorded in the account of the customer uniquely identified by the SIM card [4].

SIM card adopts a new single chip microcomputer and memory management structure, and its processing function is greatly enhanced. The logical structure of its intelligent features is a tree structure. All characteristic parameter information is expressed in the form of data fields, and there are three kinds of data information in SIM card: one is the information related to the cardholder and all the business information that SIM card will provide in the future, which is stored in the root directory; Second, the unique information in the GSM application, such data is stored in the GSM directory; Thirdly, the information used by GSM applications is located in the telecom directory and can be shared with other telecom applications or services [4].

***5 sheets

Combined atlas

structure type

1, SIM card structure

SIM card is a smart card with a microprocessor. It consists of five parts: CPU(8 bits), RAM (working memory, 6~ 16kB), ROM (program memory, 3~8 kB), EPROM or EEPROM (data memory, 128~256 kB) and serial communication unit. These five modules are integrated in an integrated circuit.