alt Hacker NewsMaybe not general data cap exemption but for as long as I remember a lot of carriers in Europe whitelist certain apps that people think of as "essential" that work even when you've reached your data limit - such as WhatsApp and Messenger. Perhaps there are certain applications specific to South Korea that people think as essential/universal and expect them to work without a data plan (even maybe related to the digital ID thing they have there).
Here in Spain a few years ago some ISP's just put a data cap about 2.7KBPS (2-3G?) and call it a day. Enough for text sites, messages and the like. But if you were smart (mosh, NNTP)... you could connect to some public Unix servers and fire up Lynx/Links at crazy speeds under a Tmux window and be able to read sites/blog posts and the like. And with edbrowse, even comment on some simple JS sites.
With some cachés set for my audio player I could even listen to some odd Avant Gardé radio streams -think Frank Zappa like- at http://dir.xiph.org with 16 KBPS quality in OPUS format. Not totally robotic, it sounded better than old MP3's at 32KBPS.