For the record: Shinhan Bank's Global ATM located on the departure level (3rd floor) at ICN did not charge any fees for withdrawals with a foreign credit card (PLUS network). Maximum amount indicated was KRW 300,000.
ATMs at the arrivals level (ground level) showed a KRW 4,000 fee for withdrawals on the last confirmation screen of the transaction (which could still be cancelled at that point).