What cell phone coverage can i get in Korea?

SK, LG, and KT. I've had the best coverage with SK. If you aren't in the middle of no where they all work pretty well. If you plan on getting on with SK or LG as a foreigner it will cost you a huge deposit. With KT you can have it billed with your house phone and internet. Also new/used phones are available that you buy cards to get minutes. That's what a lot of foreign folks do.