During my first visit, I thought prepaid SIM cards are not available, until I spotted a local convenience store selling such from Korea Telecom [KT].
There were only two options that time, and I bought a Nano SIM with 1 GB of data allowance. I spent around 34,000 won for it [~ $28.00].
Unlike prepaid SIM cards in other countries, the one I bought needs activation. It takes an hour as long as the online registration is completed within the local business hours.
Take note, a free WiFi or data connection is needed to register unless data roaming is activated in the originating country.
If the registration is done after the business hours, activation will be processed at 9 a.m. on the following day. No holidays are being observed for activations.
Where to Buy
To purchase a KT prepaid SIM card, just drop by a local convenience store like CU [CVS For You], 7/11, or whatever in the airport. Cash is the usual form of payment.
A KT prepaid SIM card comes with a leaflet [see featured image] which contains details, instructions, and troubleshooting steps.