Subscriber Identity Module, usually known sim information as a SIM card, is a minute processor that stores all the necessary data about the user's telecommunication service.

Fundamentally, SIM card functions as a key to accessing communication networks, allowing users to make phone calls and text messages. Moreover, it similarly helps in retaining vital contacts, messages, and even network-specific data.

There are generally three types of SIM cards available in the telecom market: the standard size, micro, and nano size. All these versions vary in physical dimensions, but offer the same functionality.

Every SIM card comes characterized by a unique IMSI number, which is comprised of a fixed length numeric sequence. This distincts each user within the network.

Moreover, each SIM card comes programmed with unique Ki key, which acts for guaranteeing communication over the telecom network.

Switching to these SIM cards' functions, they hold data like a user's mobile number, service information, and security credentials. Apart from these, they allow additional services such as call forwarding, call waiting, and voice messages.

In conclusion, it becomes evident that SIM cards are crucial elements of our mobile phones. They act like the identity proofs for our mobile networks, helping them function correctly. Knowing your SIM information assists in tackling problems related to your mobile network.

Furthermore, being knowledgeable about your SIM card can also help in making decisions regarding phone upgrades, changing service plans, and even traveling internationally.