I read a couple of threads about possibility of an iPhone 4 bought in US working in S. Korea; the answer is not possible because AT&T locks iPhones. Then what about a 4S? Would it work in S. Korea?
You'll have to get the device factory unlocked. The 4s isn't jailbreakable to depend on a gevey sim. So that's the only option for using the 4s in s.korea