How can I contact someone whose mobile phone number is in Weihai when they go to Korea?

1. Text or call: If you know the other person's mobile phone number, you can try to contact him by text or phone. The other party has opened the international roaming function, so you can dial their mobile phone number directly, otherwise you need to add the international area code +82 (South Korea's international area code) to dial.

2. Email: If you know the other person's email address, you can try to contact him by email.

3. Social media: There are accounts on social media, and you can contact them through social media, such as sending private messages or leaving messages.

4. Emergency contact: If the other party specifies an emergency contact before departure, you can contact the emergency contact and ask for help to contact the other party.