Unfortunately, it is not possible to activate your SIM card before arriving in Korea as the activation process requires verification of your ID by the Korean immigration office, which can only be done upon passing through immigration.
However, you can make an activation reservation in advance by submitting an activation request through
link.kimchimobile.com/activation. By doing so, you can secure a reservation and avoid any inconvenience at the airport.
Please note that the Kimchi Mobile SIM card activation center operates from 10 AM to 5 PM, Monday through Friday.