Before you scan anything
Do three checks while you still have dependable Wi-Fi. First, confirm that the phone supports eSIM and is carrier-unlocked. A device can show an eSIM menu and still be locked to the carrier that sold it. Second, read when the plan’s validity begins. Some providers start the clock when the profile is installed; others start it when the eSIM first connects in the covered country. Third, keep the QR code private. It is an activation credential, not a ticket to post or forward.
If the provider recommends installing before departure, do that. If installation itself starts validity and the trip is weeks away, wait until the documented window. RoamSonar compares price and disclosed plan attributes; the provider’s installation email remains the authority for that specific profile.
Install on iPhone
On a current iPhone, open Settings, then Cellular or Mobile Data, and choose Add eSIM. Select Use QR Code and scan the provider’s code from another screen or printed page. If the provider supplied manual details, choose the manual-entry option and enter them exactly. iOS will download the profile and ask you to label the line.
Use a clear label such as “Japan travel” rather than “Secondary.” Keep your normal number as the default voice line unless you intentionally want something else. Select the travel eSIM for cellular data. Turn off Allow Cellular Data Switching so the phone does not silently move data back to the home line when the travel line is weak.
Open the new line’s settings and follow the provider’s instruction for Data Roaming. Travel eSIMs commonly need roaming enabled because the profile connects through partner networks. That does not mean roaming should be enabled on your home line. Confirm the setting line by line.
Install on Android
Menu names vary by manufacturer. On many Android phones, open Settings, then Network & Internet, Connections, or SIM Manager. Choose Add SIM or Add eSIM, scan the QR code, and let the profile download. Some devices call it Download a SIM instead.
Label the profile with the destination. Set Mobile Data to the travel eSIM and disable automatic data switching or backup calling if it could use the home SIM’s data. Open the travel line and apply the provider’s roaming and APN instructions exactly. Do not copy an APN from a random forum when the provider supplied one.
Dual-SIM Android phones sometimes show separate toggles for calls, messages and data. Keeping calls on the home number while data uses the travel eSIM is usually the least disruptive arrangement. Charges for calls and texts still depend on the home carrier, so receiving a call is not automatically free.
When to activate
Installation, activation and first network connection are not always the same event. Installation adds the profile. Activation authorizes service. The validity clock may begin at installation, activation, first connection or a stated date. Read the policy before tapping through.
For Japan, RoamSonar currently compares Japan: 84 plans from 3 providers, from $2.54, best per-GB $0.76/GB. For India it compares India: 82 plans from 3 providers, from $2.54, best per-GB $0.99/GB. Those figures help choose a plan, but they do not replace the selected provider’s activation instructions. Open the Japan page or India page and inspect the activation and eKYC fields before buying.
Test without burning roaming money
After installation, make sure the travel profile appears and can be switched on. Before arrival it may show No Service, which can be normal outside its coverage. Do not repeatedly delete and reinstall it: many QR codes are single-use.
On arrival, switch on the travel line, select it for mobile data, apply the required roaming setting, and wait a few minutes. Toggle airplane mode once if it does not register. Restart only after checking the line selection. If the provider gives an APN, confirm it character for character.
Test with a small webpage before opening photo backup, app updates or video. Then verify that the home line’s data counter is not increasing. A screenshot of the SIM settings can help support diagnose the problem without exposing the QR code.
Common failures
- “Unable to add eSIM” can mean the code was already used, the phone is locked, the device lacks support or the provider has not released the profile.
- Installed but no service often means the destination has not been reached, data roaming is off on the travel line, the APN is missing or the wrong line owns mobile data.
- Calls work but data does not usually points to line selection, roaming or APN settings.
- Data works but disappears in a hotspot can mean tethering is restricted; filter for hotspot before purchase instead of assuming.
Keep a recovery path
Save the provider’s order number, support route and manual installation details offline. Keep airport or hotel Wi-Fi credentials available. Do not delete the profile until support confirms that deletion is safe. If you must contact support, send the order reference and error text, never the full QR code in a public channel.
Once connected, turn off automatic app updates and cloud photo backup if the allowance is small. The successful setup is the one that stays on the travel line, respects the activation policy and does not surprise you with home-carrier roaming.