Subscriber Identity Module, usually known as a SIM card, functions as a small chip that stores all the necessary data related to a mobile phone user's network service.

In essence, SIM card works as a copyright to accessing communication networks, allowing users to make phone calls and text messages. Moreover, it similarly helps in storing important phone numbers, text messages, and even in some cases network-specific data.

There are commonly three types of SIM cards available in the market: standard, micro size, and nano. Each of these versions vary in size, but offer similar functionality.

Every SIM card comes unique by an individual IMSI (International Mobile Subscriber Identity) number, which is comprised of a 15-digit numeric code. This distincts each subscriber within the network.

Moreover, every SIM card is equipped with unique Ki key, which acts for ensuring communication over the network.

Switching to SIM cards' role, they store data such as a user's phone number, service information, and security-related information. Apart from these, they allow additional services such as call forwarding, call barring, and website voice mail.

In closing, it becomes evident that SIM cards are crucial components of our mobile communication. They act like the identity cards for our mobile networks, allowing them function properly. Knowing your SIM information helps in solving problems related to your network service.

Moreover, being knowledgeable about your SIM card may also aid in making choices about phone upgrades, changing network service, and even in some cases travelling abroad.