Decide whether you need an app call or a telephone call
KakaoTalk is a messaging app with voice and video calls. WhatsApp, Signal, FaceTime and other services provide their own internet-calling options. Check how the other person joins; some services require an account or app, while some support invitation links.
An app call is not automatically a call to an ordinary landline, bank or airline number. For that, use your carrier or an internet calling product that explicitly supports telephone calls to the destination.
Internet calls use Wi-Fi or mobile data, so connection or roaming charges can still apply.
Check your carrier's Wi-Fi calling
Wi-Fi calling lets a supported carrier line make calls through Wi-Fi. Enable and test it before departure, because some carriers require initial activation on the home network.
Read the charges for the number you will call. For example, Verizon's Wi-Fi calling guidance says calls back to the US are free on its described unlimited talk-and-text plans, while calls to other countries can incur international charges. The terms of another carrier or plan may differ.
Confirm that the phone shows Wi-Fi calling is active. Turning off data roaming alone does not prevent a voice call from using cellular roaming and being charged.
Compare telephone-calling products
Services such as Viber Out and eligible Google Voice accounts can call supported telephone numbers through the internet. Check current country coverage, destination rates, billing increments and account eligibility before buying credit.
Some toll-free, premium or short-code numbers may not be reachable from abroad. Use the organisation's published international contact number when provided.
Do not assume a particular service is always cheapest. Compare the actual destination and your existing plan allowance.
Use the correct international number
On most mobile keypads, hold 0 to enter +, then enter the country code and the number in its published international form.
For a Korean number, remove the domestic leading zero after adding +82: 010-1234-5678 becomes +82 10 1234 5678. Other countries have their own numbering rules, so do not remove every leading zero automatically.
The international format helps a saved contact work while travelling, but it does not determine the call price.
Check landline and roaming charges
A hotel phone may require an outside-line prefix and can have its own charges. Ask for the rate before calling. Korean international carrier prefixes such as 001, 002 and 00700 select particular services; they are not limited to phones without a plus key.
For cellular roaming, check what starts a paid session. Making or answering calls, sending messages or using data can trigger charges depending on the plan. A data-only travel SIM does not replace ordinary voice service on your home number.
For an emergency in Korea, call 112 for police or 119 for fire, ambulance or rescue through an available local phone connection.
