Originally Posted by
FS_FRA
Just go to one of the counters at ICN after you exit customs and get a local eSIM there. It's inexpensive, unlimited data, and they help you set it up if required. I do that every time I'm in South Korea - I use Airalo in other places.
This is sort of what I ended up doing - except I went for a physical SIM rather than an eSIM. "Reserved" it from LG U+ in advance which gives 10% off, and it cost ~US$26 for 10 days which isn't what I'd really call cheap, but it is "unlimited" data (3GB/day at LTE speeds).
I went for the physical SIM over an eSIM for 2 reasons - one was because the eSIMs are data only where the pSIMs can also receive calls. The second is because with a pSIM the card that the SIM come in doubles as a TMoney card to use on the subway, saving a few thousand won over buying one separately. Unfortunately the voice option didn't work out, as apparently their voice SIMs don't work on Google Pixel phones, only Apple/Samsung., so I ended up with a data-only one anyway, but otherwise it worked fine.