IMEI 1 is the primary hardware identifier tied to a smartphone's first physical SIM slot, serving as the main network authentication channel. It is the master record for the entire device in the global GSMA database and carrier registries.
When performing a background check for SimLocks, financial holds, or blacklist status, you must always use IMEI 1. If a carrier blacklists this primary identifier due to theft, fraud, or unpaid balances, the GSMA registry automatically extends that ban to the secondary IMEI (IMEI 2) to prevent users from circumventing the block
