Subscriber Identity Module, usually known as a SIM card, functions as a minute processor that holds essential information related to an individual's network service.

At its core, SIM card works as a key to accessing communication networks, enabling consumers to send and receive calls. Moreover, it similarly helps in keeping vital 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: standard, micro size, and nano size. All these variants vary in physical dimensions, but produce equivalent capabilities.

Every SIM card comes identified by unique International Mobile Subscriber Identity (IMSI) number, which is comprised of a 15-digit numeric sequence. This differentiates each user within the cellular network.

Moreover, every SIM card comes configured with a specific Ki (Authentication Key), which is used for ensuring transmission over the network.

Talking about SIM cards' functions, they retain details like a user's contacts, service details, and security credentials. Apart from this, they allow additional services such as call advancing, call holding, and voice messages.

In summary, it's clear that SIM cards are essential parts of our mobile phones. They act like the IDs for our mobile networks, allowing them work properly. Knowing your SIM information assists in tackling problems related to your network service.

Additionally, having knowledge about your SIM card can also help in streamlining choices about phone upgrades, moving service plans, and even get more info international travel.