CDMA in S. Korea only (and N. America). Japanese system different than the rest of the world.

The rest of the world GSM.

Or buy a gsm phone at home. Voicestream in USA I think there's some others too, or International prepaid from Swisscom.

Be cautious if you want to use SIM from other company - SIM Blocked. Also make sure phone is the right frequency (900/1800 Intl; 1900 N. America). I Recommend world phone although I have 1800 Nokia for Intl and several 1900's for home.

good luck