If you use your regular smartphone while traveling in Japan, you may incur high overseas roaming charges depending on your contract.
Particularly, you should be cautious about automatic mobile data connections, background app communications, automatic photo backups, calls, and SMS.
Even if you think you are not using your smartphone much, the device may automatically connect to overseas networks, resulting in communication charges.
When using a Japan eSIM, if you mistakenly configure the settings between your regular SIM and the Japan eSIM, data communication may occur using the original SIM.
This article explains the roaming settings you should check to prevent high smartphone bills while traveling in Japan, detailing instructions for both iPhone and Android. It also introduces settings for safely using the Japan eSIM and points to consider for calls and SMS.
What is Overseas Roaming?
Overseas roaming is a system that allows you to use the SIM card from your regular service provider to connect to a partner network in your destination country.
When you arrive in Japan, your smartphone may detect Japanese communication networks and connect automatically.
If your overseas roaming plan is applicable, you can use it for a fixed fee or a certain rate.
On the other hand, if you are not enrolled in an overseas usage plan or if you engage in non-eligible communications, you may incur high charges based on usage.
| Communication Type | Potential Charges | Main Points to Note |
|---|---|---|
| Mobile Data Communication | High | Apps may communicate automatically |
| Outgoing Calls | High | Be cautious of international and overseas roaming call charges |
| Incoming Calls | May occur | Receiving calls may incur charges overseas |
| SMS Sending | May occur | Be aware of differences with messaging apps |
| SMS Receiving | Depends on the service provider | Check contract conditions for receiving authentication SMS |
| Wi-Fi Communication | Usually does not occur | Be cautious of automatic switching to mobile networks |
The charges and conditions for overseas roaming vary depending on the service provider and plan you are contracted with.
Before departing for Japan, please check the overseas usage fees, eligible countries, how to start using it, and the maximum amount.
Main Causes of High Smartphone Bills
Data Roaming is ON
If the data roaming for your regular SIM is ON, mobile data communication may occur using Japanese communication networks.
Even if you are not opening websites, communication can occur due to app notifications, email reception, location services, cloud synchronization, etc.
Automatic Switching of Mobile Data Communication
Dual SIM smartphones have a feature that automatically switches to another line based on the communication status.
If the communication of the Japan eSIM temporarily weakens and it automatically connects to the regular SIM, you may incur overseas roaming charges.
Connecting to Mobile Data After Wi-Fi Disconnects
When the Wi-Fi at hotels or airports disconnects, your smartphone may automatically switch to mobile data communication.
If your regular SIM is set as the mobile data line, you may unknowingly use overseas roaming.
Automatic Backup of Photos and Videos
If automatic backups for Google Photos, iCloud, OneDrive, etc., are enabled, photos and videos taken during your trip will be uploaded automatically.
High-quality photos and videos can consume a large amount of data, potentially leading to significant communication usage in a short time.
Automatic Updates of Apps and OS
If the smartphone's OS or apps are updated over mobile data, it may use a large amount of data.
Automatic Video Playback
If videos are automatically played in social media or news apps, just viewing the screen can consume data.
Receiving Calls Overseas
During overseas roaming, charges may apply not only when making calls but also when answering incoming calls.
Charges may also apply for forwarding to voicemail or checking messages, so be sure to check your contract conditions.
Basic Settings to Prevent High Charges
To prevent high charges while traveling in Japan, it is important to clearly separate the settings for your regular SIM and the travel Japan eSIM.
Here are some basic setting examples when using the Japan eSIM.
| Setting Item | Regular SIM | Japan eSIM |
|---|---|---|
| Line | ON if SMS reception is needed | ON |
| Mobile Data Communication | Not used | Used |
| Data Roaming | OFF | ON depending on product conditions |
| Automatic Switching of Mobile Data | OFF | |
| Regular Calls | Check charges before use | Not available for data-only products |
For the Japan eSIM, some products may require you to turn ON data roaming depending on the connection mechanism.
If you think "turning ON roaming will lead to high charges" and turn it OFF on the Japan eSIM side, you may not be able to connect to the internet.
The important thing is to turn OFF data roaming for your regular SIM and only turn it ON for the Japan eSIM as needed.
Settings to Prevent High Charges on iPhone
When using the Japan eSIM on an iPhone, you need to check both your regular SIM and the Japan eSIM.
1. Change Mobile Data Communication to Japan eSIM
- Open "Settings"
- Select "Cellular"
- Select "Cellular Data"
- Select Japan eSIM
Make sure that the check is on the Japan eSIM, not the regular SIM.
2. Turn OFF Automatic Switching of Mobile Data Communication
- Open "Settings"
- Select "Cellular"
- Select "Cellular Data"
- Turn OFF "Allow Cellular Data Switching"
If this feature is ON, when the Japan eSIM's connection weakens, it may automatically switch to the regular SIM.
3. Turn OFF Data Roaming for Regular SIM
- Open "Settings"
- Select "Cellular"
- Select the Regular SIM
- Turn OFF "Data Roaming"
4. Check Data Roaming for Japan eSIM
- Open "Settings"
- Select "Cellular"
- Select Japan eSIM
- Set "Data Roaming" according to the product description
If the product description for the Japan eSIM states to turn ON data roaming, only turn it ON for the Japan eSIM.
5. Check Wi-Fi Assist
iPhones have a feature that uses mobile data to assist when the Wi-Fi connection is poor.
If the mobile data line is set to the Japan eSIM, it will usually use the capacity of the Japan eSIM.
However, to prevent setting errors, please double-check the mobile data communication line before your trip.
Settings to Prevent High Charges on Android
On Android, the names of the setting screens may vary depending on the manufacturer and model.
Generally, you can set it from "Network & Internet," "Connections," "SIM Manager," etc.
1. Change Mobile Data Communication to Japan eSIM
- Open "Settings"
- Select "Network & Internet" or "Connections"
- Select "SIM" or "SIM Manager"
- Select Japan eSIM for Mobile Data Communication
2. Turn OFF Data Roaming for Regular SIM
- Select the Regular SIM
- Turn OFF "Roaming" or "Data Roaming"
3. Check Roaming for Japan eSIM
- Select Japan eSIM
- Turn ON or OFF data roaming according to the product description
4. Turn OFF Automatic Switching of Data
Depending on the model, it may be displayed as "Automatic Switching of Mobile Data," "Backup Calls," or "Data Switching."
Please turn it OFF to prevent automatic switching to the regular SIM even if the connection of the Japan eSIM is weak.
5. Set Data Usage Alerts
On Android, you may be able to set alerts or limits for mobile data usage.
Setting it according to the capacity of the Japan eSIM will help you notice unexpected data usage more easily.
Is it Okay to Turn ON Data Roaming for Japan eSIM?
If the product description for the Japan eSIM instructs you to turn ON data roaming, you should use it with the Japan eSIM turned ON.
Some travel eSIMs have a mechanism to connect to partner networks within Japan.
However, be careful not to turn ON data roaming for your regular SIM.
Always check which line you are operating in the settings screen.
- Regular SIM: Data Roaming OFF
- Japan eSIM: Data Roaming ON according to product conditions
- Mobile Data Communication: Japan eSIM
- Automatic Data Switching: OFF
For detailed settings for the Japan eSIM, please refer to the eSIM Setup Guide.
Should I Turn OFF My Regular SIM?
If you want to ensure that high charges do not occur, you can temporarily turn OFF your regular SIM line.
However, turning OFF your regular SIM may prevent you from using the following features:
- Receiving calls to your registered phone number
- Receiving SMS authentication codes
- Making calls using your regular phone number
- Receiving notifications from your service provider
If you need SMS authentication for banks, credit cards, or social media, you can keep your regular SIM ON and just turn OFF data roaming.
However, be aware that charges for voice calls and SMS may still apply, so check the conditions with your service provider.
Can I Prevent High Charges by Using Airplane Mode?
Turning ON Airplane Mode stops mobile communication, calls, and SMS.
If you only want to use free Wi-Fi, turning ON Airplane Mode and then turning ON Wi-Fi can help prevent charges from mobile data communication.
However, when using a Japan eSIM, you will need mobile communication, so you cannot keep Airplane Mode ON at all times.
When using the Japan eSIM, please check the data roaming and mobile data communication settings for each line.
How to Prevent High Charges from Calls
Avoid Making Regular Phone Calls
If you make calls from your regular phone number while overseas roaming, you may incur high call charges.
For contacting family and friends, using internet calls like LINE or WhatsApp can help reduce regular call charges.
Be Cautious of Incoming Calls
Overseas, charges may apply to the person answering the call as well.
For unnecessary calls, do not answer and consider contacting via messaging apps after connecting to Wi-Fi or the Japan eSIM.
Check Voicemail Settings
Even if you do not answer the phone, charges may apply for forwarding to voicemail or checking messages.
Please confirm with your service provider before departure.
If You Want to Call Within Japan
With a data-only eSIM, you cannot make calls using a regular phone number.
If you need to call hotels, restaurants, or stores, consider a phone number eSIM.
Points to Note Regarding SMS Charges and Authentication
The conditions for sending and receiving SMS vary by service provider.
Receiving SMS may be free overseas, but sending may incur charges.
Additionally, travel data-only eSIMs do not come with a phone number, so you cannot receive SMS authentication codes with that eSIM.
If you may need re-authentication for LINE, WhatsApp, banks, or credit cards, keep your regular SIM active or complete authentication before your trip.
How to Reduce Background Communication
Turn OFF Automatic Photo Backup
From the settings of Google Photos or iCloud, turn OFF photo and video uploads over mobile data.
Perform backups when connected to reliable Wi-Fi, such as at hotels.
Stop Automatic App Updates
From the settings of the App Store or Google Play, stop automatic updates of apps over mobile data.
Turn OFF Automatic Video Playback
In social media apps like Instagram, Facebook, and X, turn OFF automatic video playback or set it to only occur over Wi-Fi.
Adjust Automatic Email Reception
If you may receive a large number of attachments, consider reducing the frequency of automatic email retrieval.
Use Low Data Mode
Using the low data mode on iPhone or the data saver on Android can help reduce background communication.
For app-specific data usage, please refer to the data usage estimates.
Checklist to Confirm After Arriving in Japan
After arriving in Japan and activating your Japan eSIM, please check the following items.
- Mobile data communication is set to Japan eSIM
- Data roaming for the regular SIM is OFF
- Data roaming for the Japan eSIM is set according to the product description
- Automatic switching of mobile data communication is OFF
- Wi-Fi is OFF and you can communicate using the Japan eSIM
- Data communication is not occurring with the communication icon of the regular SIM
- Automatic backup of photos and videos is stopped
- Automatic updates of apps are stopped
After setting, open Google Maps or a website to check if you can communicate normally with the Japan eSIM.
How to Check Data Usage During Your Trip
To avoid exceeding the data capacity of your Japan eSIM, please regularly check your usage during your trip.
Here are some ways to check:
- View mobile data usage on your smartphone
- Check the My Page of the eSIM sales company
- Check remaining data in the service provider's app
- Set data usage alerts
There may be discrepancies between the data displayed on your smartphone and the remaining data on the eSIM service side.
For the final remaining data, please check the management screen or instructions of the purchased service.
If the Japan eSIM Does Not Connect
If you have turned OFF roaming for your regular SIM and still cannot communicate with the Japan eSIM, please check the following items.
- Is the Japan eSIM line ON?
- Is the Japan eSIM selected for mobile data communication?
- Is data roaming for the Japan eSIM ON?
- Is the APN set correctly?
- Is it the start date for use?
- Have you exhausted your data capacity?
- Toggle Airplane Mode ON and OFF
- Restart your smartphone
Even if you cannot communicate, do not delete the eSIM immediately based on your own judgment.
The QR code can only be used once, and there is a possibility that you cannot reinstall it after deletion.
For detailed troubleshooting methods, please refer to Troubleshooting When the Japan eSIM Does Not Connect.
Reasons Why Japan eSIM is Recommended for Those Worried About High Charges
Japan eSIMs often come as prepaid products with predetermined usage days and data capacity at the time of purchase.
Therefore, compared to overseas roaming with your regular SIM, it is easier to understand communication costs before your trip.
- You can check the fees before purchase
- You can choose according to the number of travel days
- You can use it with a set data capacity
- No need to replace a physical SIM
- Can sometimes be used in conjunction with your regular SIM
- No need to pick it up at the airport
However, even when using a Japan eSIM, if you misconfigure the settings for your regular SIM, you may incur overseas roaming charges.
Do not be complacent just because you activated the Japan eSIM; always check your mobile data communication and roaming settings.
The basic mechanism of the Japan eSIM is explained in the Complete Guide to Japan eSIM.
Selecting a Japan eSIM that Matches Your Travel Days
When using a Japan eSIM to avoid high overseas roaming charges, choose a capacity that matches your travel days and purpose.
| Travel Style | Recommended Capacity | Main Uses |
|---|---|---|
| Short trip of 1-3 days | 1-3GB | Maps, transit guides, messaging |
| General trip of 5-7 days | 3-5GB | Maps, social media, translation, search |
| Trip of 1-2 weeks | 5-10GB | Daily maps, social media, photo posting |
| Frequent video watching | 10-20GB or more | Videos, social media, video calls |
| Work or tethering | Large capacity or unlimited | Online meetings, computer connection |
For how to choose capacity and usage days, please check Japan eSIM Pricing and Plan Comparison.
You can choose from currently available products at Japan eSIM Products and Pricing Plans.
Frequently Asked Questions About High Smartphone Bills
If I turn OFF Data Roaming, will I not incur charges?
It becomes easier to prevent roaming charges from mobile data communication.
However, separate charges may apply for making and receiving calls, SMS, and voicemail.
Is it okay to have Data Roaming ON for Japan eSIM?
If the product description instructs you to turn it ON, only turn it ON for the Japan eSIM.
Please keep the data roaming for your regular SIM OFF.
Is it okay to keep my regular SIM ON?
If you set mobile data communication to the Japan eSIM and turn OFF data roaming and automatic line switching for your regular SIM, it may be possible to use both.
However, please check the conditions for calls and SMS charges with your service provider.
Will turning ON Airplane Mode completely prevent high charges?
While Airplane Mode is ON, mobile communication is stopped, making it easier to prevent roaming communication.
However, you will also be unable to use mobile communication via the Japan eSIM.
Can charges occur even if I only use Wi-Fi?
Typically, roaming charges do not occur with Wi-Fi itself.
However, if Wi-Fi disconnects and it automatically connects to the regular SIM, mobile communication charges may apply.
Will I incur charges just for answering a call?
In overseas roaming, charges may apply to the person answering the call as well.
Please check the overseas call charges with your service provider.
Will I incur charges just for receiving an SMS?
It varies by service provider and contract. Generally, receiving may be free, but always check the contract conditions.
What should I do if I incur high charges?
First, check the usage statement from your service provider to see whether the charges are from data communication, calls, or SMS.
If you have no idea, please contact your service provider as soon as possible.
Will deleting the eSIM stop communication charges?
Please turn OFF that line before deleting the eSIM.
Travel eSIMs may not be reinstallable after deletion, so it is recommended not to delete them before the end of use or during troubleshooting.
For other inquiries, please refer to Frequently Asked Questions about eSIM.
Conclusion: Turn OFF Roaming for Your Regular SIM and Set Japan eSIM for Data Communication
To prevent high smartphone bills while traveling in Japan, it is crucial to prevent unintended overseas roaming with your regular SIM.
When using the Japan eSIM, please check the following settings:
- Set mobile data communication to Japan eSIM
- Turn OFF data roaming for your regular SIM
- Set data roaming for the Japan eSIM according to the product description
- Turn OFF automatic switching of mobile data communication
- Stop automatic backup of photos and videos
- Stop automatic updates of apps and OS
- Check charges for making and receiving calls and SMS overseas
In particular, be careful not to have data roaming ON for both your regular SIM and the Japan eSIM.
If SMS authentication is not required, turning OFF the regular SIM line itself can help prevent data roaming more effectively.
By correctly setting up the Japan eSIM, you can use Google Maps, transit guides, social media, messaging, etc., while keeping track of communication costs before your trip.
You can check the purchase and pricing plans for the Japan eSIM at Japan eSIM Products and Pricing Plans.
