SIM card, usually known as a SIM card, functions as a small chip that stores all the necessary data related to an individual's subscription.

In essence, SIM card acts as a copyright to accessing a cellular network, allowing mobile phone owners to send and receive calls. Moreover, it also aids in retaining important phone numbers, text messages, and even in some cases data specific to the network.

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

Each SIM card is characterized by unique International Mobile Subscriber Identity (IMSI) number, which is consists of a fixed length numeric sequence. This distincts each user within the cellular network.

Moreover, every SIM card is configured with an individual Ki key, which acts for guaranteeing data exchange over the service provider's network.

Switching to the SIM cards' role, they retain information like a user's mobile number, service details, and security credentials. Apart from this, they allow additional services including call diverting, call barring, and voice messages.

In summary, it's clear that SIM cards are essential parts of our telecommunication services. They act like the identity proofs for our phones, making them operate efficiently. Knowing your SIM information helps in tackling any issues related to your mobile network.

Additionally, sim information being knowledgeable about your SIM card can also aid in streamlining decisions about upgrading your phone, changing network service, and even travelling abroad.