How to Use Your Home SIM and Vietnam eSIM at the Same Time (Dual SIM Guide)

Traveling to Vietnam is exciting, but staying connected while abroad can be confusing. Many travelers face the same question: “How can I keep my home number active while using cheap local data in Vietnam?”

The answer is simple: use Dual SIM technology. This guide will instruct you how to use your home SIM and Vietnam eSIM at the same time the best way.

I. Why Dual SIM (Physical SIM + eSIM) is the Best Choice for Travelers to Vietnam

Using two different network lines on one phone isn’t just convenient, it is the smartest way to manage communication and costs while abroad. However, a “Dual SIM” doesn’t have to mean “two physical cards.” The modern Dual SIM setup – one physical SIM + one eSIM.

With a dual SIM setup – typically one physical SIM (your home SIM) and one eSIM (your Vietnam data SIM) – you can enjoy both worlds:

1. Avoid roaming fees

Roaming charges from your home carrier can be extremely expensive. Data roaming sometimes costs $10–$20 per day, even for basic browsing. For example, by installing a Vietnam eSIM from vietnamesim.com, you can use local Vietnamese networks at a fraction of that price – while keeping your home SIM active for essential messages.

2. Keep your primary number active

If you need to log into your bank, email, or social media, you almost certainly need to receive a security code (OTP) via SMS to your home number.

With Dual SIM, your home number stays connected to its network for texts and calls, ensuring you can always receive these crucial messages.

3. Access fast, affordable local data in Vietnam

You don’t have to wait in line to buy a physical SIM card, deal with language barriers, or swap out tiny chips. You can purchase, install, and activate your Vietnam eSIM before you fly – completely online. Once you land in Vietnam, your data connection is ready instantly.

4. No More SIM Swapping Hassle

Old travel routines required removing your SIM card, risking loss or damage. With an eSIM, everything is digital. You just scan a QR code, download your Vietnam data plan, and start using it immediately.

II. Essential Prerequisites: Your Dual SIM Checklist

Before you purchase your Vietnam eSIM, make sure you meet these three requirements.

1. Phone must be eSIM compatible

To use dual SIM with an eSIM, your phone must be equipped with eSIM technology.

• iPhone: XS, XR, SE (2nd Gen), 11, 12, 13, 14, 15 series and newer
• Samsung: Galaxy S20, S21, S22, S23, Z Fold, and Note series
• Google Pixel: 3 and above
• Other brands: Check “eSIM” in your phone’s settings

Self-Check Tip:

• Go to Settings > Cellular / Mobile data / SIM manager
• If you see an option to “Add eSIM” or “Add Cellular Plan,” your phone is compatible.

2. Phone Must Be Unlocked

This is the single most important rule for travel SIMs. Your phone must be “carrier-unlocked” by your home service provider to use an eSIM from a different mobile network carrier.

How to Check:

• Go to Settings > General > About
• Look for a “Carrier Lock” or “SIM Restriction” status.
• It should say “No SIM restrictions” or be blank. If it says your carrier’s name, you must contact them to unlock the phone before traveling.

IV. Step-by-step guide to set up dual SIM (Home SIM + Vietnam eSIM)

Follow these 4 critical steps to ensure your Home SIM stays for calls/texts and your Vietnam eSIM handles all data.

Step 1: Install the Vietnam eSIM

With a QR code or activation code sent from your eSIM provider, you can start setting up your Vietnam eSIM. You can do this while connected to Wi-Fi at home or at the airport before you fly.

1. Go to your phone’s Settings >Cellular/Mobile Data.
2. Select Add eSIM or Add Cellular Plan.
3. Choose Use QR Code and scan the QR code you received from the eSIM provider. If not, enter your given activation code manually.
4. Follow the prompts to install the new eSIM plan.

Crucial Tip: When prompted, DO NOT set the new Vietnam line as your primary or default data line yet, and DO NOT turn on Data Roaming for this line until you arrive in Vietnam.

Step 2: Label Your SIM Lines Clearly

Your phone will now have two active lines. Labeling them correctly prevents you from accidentally using the wrong line.

1. Go back to Settings > Cellular/Mobile Data.
2. Tap on your Home SIM and rename it (e.g., “Home (OTPs Only)“).
3. Tap on the new eSIM and rename it (e.g., “Vietnam eSIM“).

Step 3: Configure Default Line Settings (Crucial)

This is the step where you tell your phone what job each SIM should do.

To avoid roaming fees and confusion, set up your preferences carefully:

• Mobile Data: Select Vietnam eSIM
• Calls & Messages: Keep Home SIM
• Data Roaming: Turn off for Home SIM

This lets you use cheap local data while keeping your main number active.

Step 4: Final Activation Upon Arrival in Vietnam

Once your plane lands in Vietnam:

1. Go to Settings > Cellular/Mobile Data.
2. Tap on the Vietnam Data line.
3. Toggle the line to ON.
4. Turn ON Data Roaming for the Vietnam Data line. (This is normal for prepaid international eSIMs to connect to the local Vietnamese network).

Note: The activation rule of Vietnam eSIM varies by eSIM provider. Some are automatically activated right upon getting connected with the supported network, while others require further steps like dialling, but it is quick and easy in general. Check your eSIM guide carefully before installing.

Within a few minutes, your phone will connect to a local Vietnamese network (like Viettel or Vinaphone or MobiFone). Your Home SIM will remain active for calls and texts, and all your internet use will now be covered by your affordable Vietnam eSIM plan!

Vietnamesim.com provides a wide range of eSIM plans for travelers to Vietnam, from local networks, durations to features – meeting all demands of travelers worldwide.

• Viettel eSIM – top 1 Vietnam
• Vinaphone eSIM
• MobiFone eSIM (Official network)
• MobiFone Skyfi eSIM
• MobiFone Local eSIM
• Vietnam eSIM 15 days
• Vietnam eSIM 20 days
• Vietnam eSIM 30 days
• Vietnam eSIM data-only
• Vietnam eSIM with phone number

V. How to Manage Your Dual SIM Setup

1. Handle Outgoing Communication

Data: Your apps (maps, social media) will automatically use the Vietnam eSIM data.

Calls/Texts: When you try to make an outbound call or send a text, your phone will prompt you to choose which line to use (Home or Vietnam). Always select the Home line for OTPs/emergency calls. For general communication, use Wi-Fi or VoIP apps (like WhatsApp, Zalo, or Facebook Messenger) over your fast eSIM data.

2. Monitor Data Usage

Regularly check your data usage in your phone’s settings to ensure you have enough allowance on your Vietnam eSIM. Your Home SIM data usage should remain at 0 (or near $0$).

3. Battery Consumption

Running two active connections can sometimes drain your battery slightly faster than running one. If you find your battery life is too short, you can temporarily turn off the Home line entirely when you don’t expect urgent texts or calls, keeping only the Vietnam Data line active.

VI. Troubleshooting Common Issues with dual SIM

1. eSIM not activating or showing “No Service”

• Restart your device.
• Make sure data roaming is turned on for Vietnam eSIM.
• Confirm your eSIM installation completed fully.

2. Dual SIM conflicts (when both try to use data)

Go to data settings and choose one SIM as your data line.

3. Need to re-download or transfer your eSIM

If you have not scanned the QR code yet, you can transfer your eSIM to a new device. Of course. But if you scanned it or entered the activation code, the capability of transferring a Vietnam eSIM (or any other travel eSIM) depends on the policy of the provider. Contact the support team for details.

VII. FAQs