Updated: 2026-03-24 15:37:15
"I always mess up my phone settings by accident—what if I install the eSIM wrong?"
"I'm not tech-savvy, and just hearing about scanning QR codes makes me nervous..."
Don't worry—these concerns are really common on Reddit travel forums. But here's the good news: installing an eSIM is half done if you know how to scan a QR code. Just avoid these few common pitfalls, and you'll easily enjoy Japan's high-speed 5G network.
This is the most searched question on Google and most discussed topic on Dcard. The answer: It depends on whether you bought a "local carrier" or "international roaming" eSIM!
As long as you've selected the correct "Mobile Data" source, turning on roaming won't cause your original carrier to charge you excessive fees—feel free to enable the connection.
💡 Pro Tip: Roaming-type eSIMs need to route data back to third-party country/region servers (like Hong Kong or Singapore), which creates physical distance "latency." If you want smooth Google Maps navigation and high-quality video streaming, a native connection directly to Japan's docomo local infrastructure is the best solution.
After installing your eSIM, remember to check your iPhone or Android's "Mobile Service" settings.
While your phone supports dual SIM dual standby, to avoid interference or the system accidentally switching back to your original data plan, we strongly recommend turning off your original physical SIM card.
This not only ensures 100% of your data comes from the eSIM, but also eliminates the risk of accidental international roaming charges.
Most eSIMs start counting their validity period from the moment you "scan and activate."
If you're buying a Japan local eSIM like CDJapan Rental, please scan it after arriving in Japan or right before departure to avoid wasting valuable usage days.
Installing an eSIM requires a stable internet connection.
It's recommended to use your home's stable network before departure to download and set up the eSIM, or after arriving in Japan, connect to the airport's free WiFi first before setting up. This significantly reduces the chance of installation failure.
Go to "Settings → Mobile Service" and set your newly installed eSIM as the "Primary Mobile Data." Many users report "having signal but can't access the internet"—this is usually because the primary data source is still set to their original number.
You don't need to be a tech expert—just know how to scan a QR code and follow the steps to confirm "Data Roaming" and "Data Source," and you'll definitely get it set up successfully.
Once you've done it successfully once, next time you go to Japan you'll realize: this is so much more convenient than swapping physical SIM cards! 😉
