eSIM vs Local SIM for Japan, Vietnam & Southeast Asia

Landing connected changes the first few hours of a trip completely: you can call a ride, load a map, and message your accommodation without hunting for airport Wi-Fi. Here's how to decide between an eSIM and a local SIM.

First, check your phone

• Most phones from recent years support eSIM, but carrier-locked handsets often do not. Check before you buy anything.
• Confirm the phone is unlocked for use with other networks.
• Find where eSIMs are added in your settings once, at home, so you're not learning it in an airport.

eSIM — the convenient option

Buy online before you fly, install it over Wi-Fi at home, and activate it on landing.

Best for: short trips, multi-country routes, and anyone who wants zero friction on arrival.

• You keep your home number active on the physical SIM for banking codes and two-factor messages.
• Regional plans covering several countries are useful for a multi-stop route.
• Almost all traveller eSIMs are data-only — no local phone number for calls or SMS.

Local SIM — the cheaper option

Bought at an airport counter or a phone shop in town.

Best for: longer stays, heavy data use, and anywhere you need a local number.

• Airport counters in Vietnam and Thailand are quick and inexpensive.
• Japan's visitor SIMs are pricier, and pocket Wi-Fi rental is a common alternative there.
• Registration usually requires your passport.

How much data you actually need

Maps, ride-hailing and messaging use surprisingly little. Video calls, uploading photos and streaming use a great deal. If you post video from the road, buy more than you think; if you don't, the smallest plan is usually enough.

Practical checks on arrival

1. Turn data roaming on for the travel eSIM — this catches people out constantly.
2. Turn data roaming off for your home SIM, so it can still receive texts without charging you for data.
3. Set the travel line as the default for mobile data.