Traditionally, SIM cards were used for transferring data between devices. In the past, SIM cards were used to store many different types of data, such as:
User data
Contacts
SMS messages
Dialed calls
Network data
Integrated Circuit Card Identifier (ICCID): Serial number of the SIM
International Mobile Subscriber Identity (IMSI): Identifier that ties the SIM to a specific user account
Location Area Identity (LAI): Identifies the cell that a user is in
Authentication Key (Ki): Used to authenticate to the mobile network
Various other network-specific information
With the rise in capacity of device storage, SD cards, and cloud backups, the necessity for storing data on a SIM card has decreased. As such, most modern smartphones typically do not store much, if any, user data on the SIM card. All network data listed above does still reside on the SIM, as a SIM is necessary to connect to all modern (4G) cellular networks.
As with all...