Traditionally, SIM cards were used for transferring data between devices. SIM cards in the past were used to store many different types of data, such as the following:
- 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
- MSISDN: Phone number assigned to the SIM
- Location Area Identity (LAI): Identifies the cell that a user is in
- Authentication Key (Ki): Used to authenticate 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 previously does still reside on the SIM, as a SIM is necessary to connect to all modern (4G) cellular networks.
As with all Android devices, though, there is no concrete stipulation that user data can't be stored on a SIM; it simply doesn't happen by default. Individual device manufacturers can easily decide to write user data to the SIM, and individual users can download applications to provide that functionality. This means that a device's SIM card should always be examined during a forensic examination. It is a very quick process, and should never be overlooked.