You can get a hybrid phone (UMTS/GSM) that also has a slot for a SIM card. The European version of the Nokia 1280 is an example http://www.cellularabroad.com/japan-phone.php. Then, you can get an international roaming SIM card for that phone that works in Korea and Japan. As far as getting a country specific SIM card for Korea or Japan, no, they don't exist.