Subscriber Identity Module (SIM), usually known as a SIM card, functions as a tinny smart card that stores all the necessary data about the user's telecommunication service.

Fundamentally, SIM card works as a copyright to accessing a cellular network, allowing users to send and receive calls. In addition, it also helps in retaining crucial personal contacts, messages, and even in some cases data related to the cellular network.

There are commonly three types of SIM cards available in the market: the standard size, micro size, and nano. All these types differ in size, but produce similar functionality.

Every SIM card is identified by an individual IMSI number, which is consists of a fixed length numeric code. This differentiates every individual within the cellular network.

Moreover, each SIM card is equipped with an individual Authentication Key (Ki), which serves for guaranteeing transmission over the network.

Switching to the SIM cards' functionalities, they retain data like your contacts, service details, and security data. Apart from this, they allow additional services like call diverting, call holding, and voice mail.

In summary, it's clear that SIM cards are essential elements of our mobile phones. They act like the IDs for our phones, making them work properly. Knowing your SIM information helps in solving issues related to your mobile network.

Furthermore, understanding your SIM card can also aid in facilitating choices about upgrading your phone, changing network service, and get more info even international travel.