Short answer
Select the travel eSIM for mobile data, turn data roaming on for that line, and check the home line's roaming and automatic data switching separately to avoid its data charges. Apple and Google show the settings for the data line and for roaming.
Fact table
As of 2026-10-20
Each claim names its source. The full source list, with the date each page was read, is below.
| Claim | Source |
|---|---|
| Wakamo's help page says: when you are ready to use your plan, select the travel eSIM for mobile data and turn data roaming on for that line. Check the home line's roaming and automatic data switching separately to avoid its data charges. | Wakamo help |
| The same page says an installed eSIM does not always mean it is connected. To test mobile data, briefly turn Wi-Fi off and open a webpage. | Wakamo help |
| On iOS 26 and later, Apple says that if a travel eSIM is already on the iPhone, you might get a notification labeled Turn On Travel eSIM when you arrive. If you keep both lines, Apple says the travel eSIM is used for data, and you might still incur roaming fees from your home eSIM. You can also open Settings, tap Cellular, tap Cellular Data, and select the line. | Apple Support, travel with eSIM |
| Apple says Data Roaming permits internet access over a cellular data network outside the carrier's coverage. After arrival on a Dual SIM or Dual eSIM iPhone, turn on Cellular Data, tap the number, tap Cellular Data Options, and turn on Data Roaming. If the status bar says No Service or SOS only, Apple says to make sure Data Roaming is on, then turn Airplane Mode on for about 30 seconds and off again so the iPhone selects a network. If the date and time are wrong, turn on Set Automatically under Settings, General, Date and Time. | Apple Support, data roaming |
| Apple says one number at a time can use cellular data. Change it under Settings, Cellular or Mobile Data, Cellular Data. If Allow Cellular Data Switching is on, a voice call on the voice-only number uses that number for voice and data during the call. Apple says that switch does not work while Data Roaming is on, and that fees may apply. If the switch is off, cellular data does not work during a call on the number that is not the cellular-data number. | Apple Support, Dual SIM |
| Apple's iPhone guide says to tap Cellular Data and choose the data line, then tap Default Voice Line and choose the voice line. You may incur roaming charges if Data Roaming is on and you are outside the country or region covered by the carrier's network. | iPhone User Guide, Dual SIM |
| On a Pixel 3a or later, Google says only one SIM can be the default for mobile data, under Settings, Network and internet, SIMs, then Your primary SIMs. Calls and texts are chosen there separately from data, and calls can be set to ask every time. Some of these steps work only on Android 11 and up. A Pixel 3a bought in Japan cannot have two SIMs. | Google Pixel Help, dual SIMs |
| Google says Roaming lets a Pixel send data over other carriers' networks when you leave an area your carrier covers. With more than one SIM, use the tabs at the top of mobile network settings to change each SIM. During a phone call, Google says all data goes through the SIM making the call. | Google Pixel Help, mobile networks |
| On a Pixel, Google says to turn Roaming on or off under Settings, Network and internet, SIMs. Some carriers charge extra for data roaming. Google also says data roaming may be the only way to connect to the internet in some places. | Google Pixel Help, data roaming toggle |
| Narita Airport says a Wi-Fi enabled device has access throughout every terminal and on the terminal shuttle buses. Turn Wi-Fi on, select FreeWiFi-NARITA, and agree to the terms. Narita says network speed may be affected by environments and congestion. | Narita Airport, Wi-Fi |
| Haneda Airport says free wireless LAN is available in Terminal 1, Terminal 2, and Terminal 3. Select HANEDA-FREE-WIFI, open a browser, and follow the on-screen instructions. In Terminals 1 and 2 it cannot be used in shops except lounges, and it may be difficult to connect in certain areas. In Terminal 3 it cannot be used in certain shops except lounges, and it may be difficult to connect in certain areas. | Haneda Airport, wireless LAN |
| JNTO says Japan's major international airports provide free Wi-Fi within their terminals. Besides Narita and Haneda, it names Kansai International Airport, New Chitose Airport, Centrair Airport, and Fukuoka Airport. | JNTO, Wi-Fi in Japan |
FAQ
What should I set as the mobile data line?
Wakamo's help page says to select the travel eSIM for mobile data and turn data roaming on for that line. On iOS 26 and later, if you keep both lines from Apple's Turn On Travel eSIM notification, Apple says the travel eSIM is used for data. On a Pixel 3a or later, Google says only one SIM can be the default for mobile data.
Do I turn on data roaming for the travel eSIM?
Wakamo's help page says to turn data roaming on for the travel line. On a Dual SIM iPhone, Apple says to turn Data Roaming on for the number you want, under that number's Cellular Data Options. On a Pixel, Google says to turn Roaming on or off under Settings, Network and internet, SIMs, and that some carriers charge extra.
How do I avoid my home line's data charges?
Wakamo's help page says to check the home line's roaming and automatic data switching separately to avoid its data charges. Apple says you might still incur roaming fees from your home eSIM if both lines stay on, and that roaming charges may apply when Data Roaming is on outside your carrier's coverage. On a Pixel, Google says that during a phone call all data goes through the SIM making the call.
Which line does the phone use for calls?
Apple's iPhone guide says you choose the default voice line under Default Voice Line, separate from the cellular data line. On a Pixel, Google says you choose the SIM for calls and the SIM for texts separately from the data SIM, and that calls can ask every time.
Does the eSIM connect as soon as I land at Narita or Haneda?
Neither airport page says a travel eSIM connects on landing. Narita says Wi-Fi is available throughout every terminal and on the terminal shuttle buses, on FreeWiFi-NARITA, and that network speed may be affected by environments and congestion. Haneda says HANEDA-FREE-WIFI is in Terminals 1, 2, and 3, and that it cannot be used in shops (certain shops in Terminal 3) except lounges, and may be difficult to connect in certain areas. Apple's Turn On Travel eSIM notification is something you might see on arrival on iOS 26 or later if a travel eSIM is already on the iPhone.
What if the iPhone says No Service after I land?
Apple says to turn on Cellular Data, open that number's Cellular Data Options, and make sure Data Roaming is on. Then turn Airplane Mode on for about 30 seconds, turn it off, and let the iPhone select a network. If the date and time are wrong, Apple says to turn on Set Automatically under Settings, General, Date and Time.
Sources
Wakamo helpwakamo.io
Wakamo product information. When you are ready to use the plan, select the travel eSIM for mobile data, turn data roaming on for that line, and check the home line's roaming and automatic data switching separately to avoid its data charges. Briefly turn Wi-Fi off and open a webpage. An installed eSIM does not always mean it is connected.
Accessed 2026-10-20.
Apple Support, travel with eSIMsupport.apple.com
On iOS 26 and later, a Turn On Travel eSIM notification may appear on arrival if a travel eSIM is already on the iPhone. Keeping both lines uses the travel eSIM for data and may still incur home-line roaming fees. The data line can also be chosen under Settings, Cellular, Cellular Data.
Accessed 2026-10-20.
Apple Support, data roamingsupport.apple.com
Data Roaming is how an iPhone reaches the internet on a cellular network outside the carrier's coverage. After arrival, Dual SIM turns it on per number under Cellular Data Options. No Service or SOS only: confirm Data Roaming, then toggle Airplane Mode for about 30 seconds.
Accessed 2026-10-20.
Apple Support, Dual SIMsupport.apple.com
One number at a time uses cellular data. Allow Cellular Data Switching moves data onto the voice line for the length of a call, and Apple says that switch does not work while Data Roaming is on.
Accessed 2026-10-20.
iPhone User Guide, Dual SIMsupport.apple.com
Choose the cellular-data line and the default voice line separately. Roaming charges may apply when Data Roaming is on outside the carrier's coverage.
Accessed 2026-10-20.
Google Pixel Help, dual SIMssupport.google.com
On Pixel 3a and later, one SIM is the default for mobile data. Calls and texts are chosen separately. A Pixel 3a bought in Japan cannot have two SIMs. Some steps need Android 11 or later.
Accessed 2026-10-20.
Google Pixel Help, mobile networkssupport.google.com
Roaming lets the Pixel send data on other carriers' networks outside the carrier's coverage. With more than one SIM, each SIM's network settings are on their own tab. During a call, data goes through the SIM that is on the call.
Accessed 2026-10-20.
Google Pixel Help, data roaming togglesupport.google.com
On a Pixel, Roaming is turned on or off under Settings, Network & internet, SIMs. Some carriers charge extra for data roaming. Data roaming may be the only way to connect in some places.
Accessed 2026-10-20.
Narita Airport, Wi-Finarita-airport.jp
Free Wi-Fi throughout every Narita terminal and on the terminal shuttle buses, network name FreeWiFi-NARITA. Narita says network speed may be affected by environments and congestion.
Accessed 2026-10-20.
Haneda Airport, wireless LANtokyo-haneda.com
Free wireless LAN in Haneda Terminals 1, 2, and 3 on HANEDA-FREE-WIFI. Shop and weak-area limits differ by terminal.
Accessed 2026-10-20.
JNTO, Wi-Fi in Japanjapan.travel
JNTO says Japan's major international airports provide free Wi-Fi in their terminals, and names Kansai, New Chitose, Centrair, and Fukuoka as well as Narita and Haneda.
Accessed 2026-10-20.