Originally Posted by Auracon
Even if you, say, have a UMTS (WCDMA) phone that works either in Europe or in the US, due to difference in network configurations between South Korea and other countries the UMTS phone would not get service there as well. This is because Korean UMTS network utilizes different bands for up/down streams and other factors.
This is untrue - SK Telecom offers WCDMA roaming for international customers (see
SK's WCDMA roaming page). The point of this discussion, as I understand it, is that there's no way to avoid paying the high roaming charges by buying a local SIM, as is commonly done elsewhere.