When I was in Seoul a year ago for the first time I was suffering a bit as Korea is one of the few countries I traveled to that didn't have prepaid SIMs for mobile Internet access. But the world keeps changing, I thought, so before going to Seoul again recently I did a quick search on the Internet if the situation had changed. And indeed it had, there's now a KT Telecom MVNO called Evergreen offering prepaid voice and data services with SIM cards that can be bought in convenience stores at the airport. Eureka!
Of course I tried it out and the basic steps described here are quite simple. Following the instructions it took me only a few minutes to buy the SIM card for 30.000 Won (€21) with a balance of the same amount on it at Incheon airport. After a couple of minutes and one or two device reboots, again as per the instructions, the phone registered with the network. Fortunately the phone configured the APN on its own as there was no mention of it in the instructions. So far so good. In the default configuration, the 30.000 Won are good for around 590 MB of data (55.8 Won per MB) which is quite a lot already.
To get a higher data volume from the credit on the SIM it is possible to activate a data package, e.g. the 1GB package for 16.500 Won. This is were things get a bit tricky. The first step is to download the “Evergreen Mobile Services” App from the app store (Evergreen is the name of the MVNO on the KT Olleh network). The app can then be used to activate the data package. Unfortunately once that is done, Internet connectivity is cut because the service expects the user to top up this amount or to move the amount from the 30.000 Won from the voice bucket to the data bucket. The later operation can be done with the App but only if you find an alternative Internet access over Wi-Fi, as the connection was cut due to the activation of the bundle. No, that does not make sense and it's very inconvenient, but that's how it worked for me. After finding an open Wi-Fi access point I could then transfer the credit from the voice bucket to data bucket with the mobile app and Internet connectivity was restored instantly. A nice side benefit of activating the data option is that the remaining balance of the SIM card can be used for voice calls without cutting into the available data volume. So instead of 3 Euros a minute to Europe I only paid around 46 cents.
Apart from this slight activation hickup, the service worked well and I always got throughput rates of several megabits per second when I tired. So if the 590 MB are sufficient for your trip, don't bother with the activation of the data option. If you want more, make sure you have a Wi-Fi hotspot available before you attempt to activate a data bundle.