Thank you Awal. However, it's not clear to me whether the phone you are referring to was a 3G phone. If I am not mistaken, not all quad-band phones are 3G phones, right?
I am aware that GSM phones don't work in Korea since I visit there about 3-4 times/year. What I was trying to find out was how difiicult it is to buy SIM cards there since I am under the impression that basically all Korean phones do not use them?