Do you know what kind of mobile apps you must download to travel to Korea? If not, I would like to recommend three apps.
I am Korean and live in France and Germany since 2010. So I am using Google maps, whatsapp something like as Western mobile apps. In 2011, I had come to Korea for Biz trip and I found that XXX maps is not working properly in Korea so I had a problem to find offices of partners. Then I asked to my sister and she shared what I have to download.
♥ Naver Map
This map is only for Korea and it is much more correct maps in Korea.
Android: https://play.google.com/store/apps/details?id=com.nhn.android.nmap&hl=en
iOS: https://itunes.apple.com/us/app/naver-map-navigation/id311867728?mt=8
♥ KaKaotalk
More than 90% of Korean use this app as Messenger.
Android: https://play.google.com/store/apps/details?id=com.kakao.talk&hl=en
iOS: https://itunes.apple.com/us/app/kakaotalk/id362057947?mt=8
♥ tripadvisor
This is an international travel app. If you want to get some reviews in English, you might need to use this app in Korea.
Hope it helps you out a bit :)
Cheers,
Lucy