If you have a Korean unlocked phone which I think you do get here or can ask for. KT gave me that. I still have my first smart phone (over 5 years - was 3G before that). But, I went to Canada before covid and put in a sim card from virgin mobile at the mall and got a local phone number for a month. Then, back in Incheon I put my Korean KT card back in. Kakao and some other apps still worked even though I had a different phone number on my phone. I bought unlimited calling and about 6 GB of data. I had to be careful to use wifi where ever I could and use up my data. Unlimited here spoils me.
