I am leaving Korea but want to keep my Korean phone number for banking apps, KakaoTalk, and other services?

Keeping a Korean number from abroad is possible but takes some setup, and it matters because so much, from banking to KakaoTalk, is tied to your number. The cleanest way is to switch to an MVNO plan with a very low monthly fee before you leave, ideally billed to a card you will keep, so the number stays active while you pay a small amount each month; some people keep a cheap maintenance plan purely to preserve the number. The catch is that most Korean carriers require an ARC for ownership, and once your ARC expires the line can become hard to keep, so plan before your status lapses. Be aware that even with the line kept, SMS verification codes only arrive if the line can receive texts, which a basic data-only or fully paused plan may not do, so choose a plan that keeps incoming SMS working for your banking and Kakao logins. Before leaving, ask your carrier or an MVNO directly about the cheapest plan that keeps both the number and incoming SMS alive, and whether it survives ARC expiry, since that is the real limiting factor.