voiceLink Roam Sim works only in unlocked mobile phones. There are cases where mobile phones purchased with subscription packages are blocked by the mobile operator. In such case contact your operator and unblock the phone.
For Japan and South Korea your mobile phone should be 3g compatible. For the rest of the world- if your phone works at home it will work abroad (it should be compatible with gsm 800/850/900/1800/1900).