Getting cash with foreign cards is difficult in Korea--most local ATMs won't take your card. You have to find the ones that bear the MC/Visa logo. They are available in airports, and pretty plentiful in Seoul, but it can be pretty tricky in small towns.

Generally, you shouldn't use a Wells Frago card abroad--the fee is $3, and they charge 2% for foreign exchange. There are much better cards out there.