This app was mentioned in 3 comments, with an average of 4.33 upvotes
후후 (whowho) is a great app for finding out who is calling you! Every Android user in Korea should have it
whowho (Android / iOS) Caller ID with a database of Korean numbers. Great for avoiding spam calls. You will need to be on wifi/data for the caller information to pop up.
Money Manager (Android only) It reads the transaction sms sent to your phone by your Korean bank, and keeps a record of it . Great for budgeting. It's made by a Korean company (app is in English if your phone is set to English), and they've coded it to correctly read the sms sent by Korean banks.
I wonder if Who Who ( https://play.google.com/store/apps/details?id=com.ktcs.whowho ) would have picked the incoming caller with a red flag?