what is a sim card used for

A SIM card, or Subscriber Identity Module, is a small chip that is inserted into a smartphone to identify and authenticate the user as a unique mobile device owner. It stores identification information that pinpoints a smartphone to a specific mobile network, including user identity, location, phone number, network authorization data, personal security keys, contact lists, and stored text messages. SIM cards allow a mobile user to use these data and the features that come with them, such as making calls, sending text messages, and accessing mobile data through the carriers network. Without a SIM card, some phones would not be able to make calls, connect to internet services such as 4G LTE and 5G, or send SMS messages. SIM cards are removable and transferable to other phones, and they have enough memory to typically store up to 250 contacts, some text messages, and other information that the carrier who supplied the card can utilize. SIM cards have come in a variety of different sizes over time, including standard, micro, and nano-SIM cards.