Subscriber Identity Module, popularly known as a SIM card, functions as a small chip that stores all the necessary data about an individual's subscription.

Fundamentally, SIM card acts as a copyright to accessing communication networks, allowing users to make phone calls and text messages. In addition, it also helps in storing important personal contacts, messages, and even data specific to the network.

There are commonly three types of SIM cards available in the market: the standard size, micro, and nano. All these variants differ in size, but offer equivalent capabilities.

Every SIM card is unique by an individual IMSI number, which is consists of a fixed length numeric code. This identifies each subscriber within the cellular network.

Moreover, each SIM card is equipped with unique Ki (Authentication Key), which is used for guaranteeing communication over the service provider's network.

Moving to these SIM cards' functionalities, they hold data such as a user's contacts, service details, and security credentials. Apart from these, they allow additional services including call diverting, call waiting, and voice mail.

In conclusion, it becomes evident that SIM cards are vital parts of sim information our mobile phones. They serve as the identity cards for our phones, allowing them work correctly. Knowing your SIM information helps in solving any issues related to your network service.

Furthermore, being knowledgeable about your SIM card may also aid in facilitating decisions regarding phone upgrades, moving network service, and even in some cases travelling abroad.