all the things I loved from my trips to seoul! (will update on busan)
Expensive but reliable: https://www.lguplus.com/ib-roaming/pc/eng
Papago - for translations
Naver Maps - I find this the easiest to use but have heard Kakao Maps has better English translation
Kakao Taxi - Sometimes cheaper than subway! Most convenient can be paid with a linked card or tmoney or cash
Uber App - this just changes into Uber T and pretty easy to use
Airalo - if you’re traveling elsewhere this is easy to get an e-sim right away