I'll be going to Seoul on Saturday. Unfortunately I don't have any international money cards. I do have two cards, an E-ON card from Unionbank (VISA Electron) and a BPI Express ATM (has a Cirrus icon). Which one would be more useful to me in Seoul?
According to this Visa site, Visa Electron is accepted in South Korea in many ATMs (make sure to choose the bank from the drop down menu). Also, According to this official site of Korean tourism Cirrus ATM cards are the most widely accepted in Korea.
It is quite hard to find ATMs that accept foreign cards, including Visa Electron and Cirrus cards in Korea outside areas with more foreign expats and tourists.
The ATMs which accept non-Korean cards will have a small logo or sign saying "Global ATM".
One of these areas with more foreigners in Seoul is Hongdae and I have found more World ATMs there each time I visit.
Citibank ATMs are not so common but there should be some in the busier part(s) of every large city, and they're your best bet.
Last time I was in Busan, the second-biggest city, I couldn't find any ATM which would accept my card other than the Citibank.