Short verdict

Buy online. Best ordered before or after travel when convenience, delivery, or luggage space matters more.

Choose an eSIM if you want mobile data as soon as you land.

What to know

Buy online before departure if your phone supports eSIM and you want data at the airport. Pick a plan by trip length, hotspot needs, and whether calls or SMS matter.

What to avoid

Skip eSIM if your phone is locked, if you need a Korean phone number for local reservations, or if your carrier roaming is already included.

Final verdict: buy online before you fly for most short Korea trips.