How to Keep Your Phone Number and Use WhatsApp with a Japan eSIM
19/11/2025 / Japan

How to Keep Your Phone Number and Use WhatsApp with a Japan eSIM

Travelling to Japan often raises a common concern: Will I lose my phone number if I switch to an eSIM? This worry stems from the fact that most travel eSIMs are data-only and do not provide a local phone number. However, your phone number is tied to your primary SIM (that you use in your home country), not to the data connection. Installing an eSIM will not overwrite or disconnect your existing number. The key is to understand how dual-SIM phones and technology work and how to set up your mobile device (phone, tablet, etc.) correctly.

A well-chosen eSIM plan can save you hundreds of pounds versus roaming fees. For example, Airalo Moshi Moshi eSIM offers 10 GB for 30 days at roughly $18 , while Esimatic unlimited day pass costs around $18.99 for 5 days. Compare this with UK carriers charging more than £6 per MB for roaming (price per MB varies depending on your home carrier). Using a travel eSIM for data and keeping your home SIM active for calls/texts lets you avoid bill shock and stay reachable on your usual number.

Note: Some links in this article are affiliate links. If you click on a link and purchase a service, I may earn a small commission at no extra cost to you. It helps me keep the blog running.



Step 1: Check Your Phone’s Compatibility and Unlock Status

Not all handsets support eSIM technology. According to our Ultimate eSIM Guide, modern phones such as the iPhone XR and later, Samsung Galaxy S20+ onwards, and Google Pixel 3 and newer models include eSIM chips. Ensure your phone is unlocked; locked devices may restrict you from using networks outside your home carrier.

  1. Check device specifications: Look for “eSIM” or “dual SIM” support in your phone’s manual or settings. If you’re unsure, search your model on the manufacturer’s website. Most of the eSIM providers display the list of supported devices in the plan details.
  2. Ensure dual SIM functionality: Dual SIM (or dual eSIM) capability allows you to run a physical SIM and an eSIM simultaneously. This feature is essential for keeping your phone number while using a your travel eSIM for data.
  3. Update your software: Make sure your operating system is up to date. eSIM features may only be available on the latest version of iOS or Android.

Step 2: Choose the Right Japan eSIM Plan

With dozens of providers, selecting a plan can be overwhelming. Focus on your data needs, trip length and budget. For cost comparisons, refer to our article on Unlimited vs Fixed Data eSIM Plans in Japan. Some examples from October 2025:

Consider how much data you will need (maps, streaming, uploads) and whether you require unlimited usage. For a one- or two-week trip with moderate use, a 10-20 GB fixed plan is usually sufficient and cheaper than unlimited options. Digital nomads may prefer unlimited plans with fair usage policies.

Step 3: Purchase and Install Your eSIM Before Travelling

Once you’ve selected a provider, buy and install your eSIM while connected to stable Wi‑Fi at home. This avoids airport stress and ensures you are ready to activate upon landing.

  1. Buy online: Visit the provider’s official site (e.g., Airalo, Esimatic, eTravelSim, Keepgo, Saily or Nomad). Check our eSIM providers page for the discounts. Choose your data plan and complete the purchase.
  2. Scan the QR code: On an iPhone, go to Settings → Mobile Data → Add eSIM (or Add Mobile Plan), then scan the QR code. On Android, open Settings → Network & Internet → SIMs → Add eSIM and either scan the QR code or enter the activation code manually.
  3. Label your eSIM: Give the eSIM a name such as “Japan eSIM” to differentiate it from your home line. Most phones allow you to label each line for easy management.


Step 4: Keep Your Physical SIM for Calls and Texts

To retain your existing phone number, do not remove your physical SIM. Each eSIM is digital and will use the second line. According to the Ultimate eSIM Guide, dual SIM allows you to keep your home plan active for calls and SMS while using the eSIM for data.

  • Disable data roaming on your physical SIM to avoid accidental roaming charges. On iPhones, go to Settings → Mobile Data → Primary SIM → Data Roaming and turn it off.
  • Set default voice and texts to your physical SIM. In dual-SIM settings, choose your physical SIM for voice calls and messages, and the eSIM for data. This ensures incoming calls/texts reach you via your usual number.
  • Test reception: Send a test SMS or ask a friend to call your number to confirm you can still receive calls and texts. If you encounter issues, check what is enabled in settings. 

Step 5: Configure Dual-SIM Settings for Data and Calls

Proper configuration ensures the right line is used for each service:

  1. Set data: Navigate to Settings → Mobile Data/Connections → SIM Manager/SIM Settings and select your Japan eSIM as the preferred SIM for data. Leave your home SIM for voice/SMS.
  2. Enable call forwarding (optional): If you prefer not to answer calls on your home number while abroad, set up voicemail or call forwarding to somebody else or a VoIP service. Some mobile operators/carriers allow forwarding to a VoIP number for free.
  3. Switch SIMs when necessary: In the SIM management menu, you can temporarily disable your home SIM to conserve battery or avoid calls during certain times. Reactivate it when needed.
  4. Prioritise networks: Some phones allow you to prioritise the eSIM for better coverage. This is helpful if your home carrier has weak signal abroad.

Step 6: Use WhatsApp with Your Original Number

WhatsApp uses your phone number for verification but doesn’t require an active SIM once set up. Therefore, after installing your eSIM:

  1. Open WhatsApp while connected to Wi‑Fi or your new eSIM data.
  2. If prompted, choose to keep your existing number. Avoid re-verifying with the new eSIM number .
  3. Continue messaging and calling as usual. Your contacts will still see your regular number.
  4. For extra security, enable two-step verification in WhatsApp (found under Settings → Account). This prevents someone else from registering your number while you’re abroad .
  5. Remember, WhatsApp calls and messages use data. So long as your eSIM has a data connection, you can call and message globally without roaming fees .

Note on other messaging (OTT) apps

The same principle applies to Telegram, Signal, Viber and FaceTime. They link to your account rather than your SIM. It means that you can keep using them over a data-only eSIM. However, if you need a to make a call to a local fixed number, consider eSIM plans that include voice and SMS services, such as Airalo Discover eSIM plan. However, these are often more expensive and not necessary for all travellers.

Step 7: Additional Tips to Stay Connected and Save Data

  • Monitor data usage: Voice and video calls on WhatsApp are efficient, but sending high-resolution videos consumes more data. Use your provider’s app to track consumption.
  • Use offline maps: Download Google Maps areas while on Wi‑Fi to reduce data usage. Consider using VPN (e.g. NordVPN or SurfShark) while connected to a public or a hotel Wi-Fi.
  • Turn off auto-update: Disable automatic app updates and background refresh for non-essential apps to conserve data.
  • Tethering usage: Most fixed-data plans allow tethering, while unlimited plans may limit hotspot usage to 500 MB/day . Check your plan’s policy before sharing your connection.
  • Backup communications: In case of technical issues, use Wi‑Fi at accommodations for voice/video calls.

Step 8: Consider eSIM Plans with Voice & SMS (Optional)

If you need a local phone number or plan to make many traditional calls, consider an eSIM plan with voice and SMS. Airalo Discover+ eSIM is a global eSIM plan that offers data, calls and SMS in multiple countries, but at higher cost.

For most tourists, using messaging (VoIP or OTT) apps suffices. Compare prices carefully; unlimited data plus voice may not be cost-effective for short trips.



Step 9: Evaluate Cost vs Convenience

Data eSIMs can drastically reduce your travel costs. A typical UK network may charge more than £6 per MB for data roaming (same applies to all other countries but with different roaming fees). In contrast, Airalo’s 10 GB plan costs about $18 (≈£14). By using your home SIM for calls/texts and an eSIM for data, you avoid roaming fees while keeping your number active.

Remember to match the plan to your usage patterns. If you’re a casual traveller who mainly uses WhatsApp and maps, fixed-data plans of 5-10 GB will suffice. For remote workers or content creators, unlimited plans with a high daily allowance may be worth the premium, but check fair usage policies.

Conclusion

You don’t have to sacrifice your phone number to enjoy affordable data in Japan. By choosing the right eSIM plan, installing it before your trip and configuring your dual-SIM settings, you can keep receiving calls and texts on your home number while enjoying cheap, high-speed data. WhatsApp and other messaging apps remain tied to your original number, so long as you don’t re-verify with the new SIM. To dive deeper into specific providers and plans, explore our dedicated reviews:

Latest articles about eSIM in Japan:

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