Dual SIM With an eSIM: Keep Your Number While Using Travel Data

Most travellers don't actually want a new phone number abroad. They want their normal number to keep working, for the bank, the family group chat and the courier back home, while their mobile data comes from somewhere other than their home carrier's roaming tariff.

That's precisely what dual SIM is for. Your home SIM and a travel eSIM sit side by side in one phone, each doing the job it's best at.

How dual SIM works on a modern phone

A dual SIM phone has two mobile lines. Usually that means your physical SIM card plus an eSIM, though many recent phones can also run two eSIMs. Each line has its own settings: it can be switched on or off, given a label, and have data roaming enabled or disabled independently of the other.

The key rule is that only one line handles mobile data at a time, while calls and texts can arrive on either. That's what makes the travel setup work: you point data at the eSIM and leave your own number in charge of calls and texts. Most dual SIM phones also show the signal for each line separately, in the status bar or the control panel, so you can see at a glance which one is connected.

HelloSIM eSIMs are data-only, so they never compete with your home number. There's no second number to confuse people, and nothing about your WhatsApp account changes.

The setup that works for most trips

Here's the configuration to aim for once you've arrived:

• Home line: switched on, used for calls and texts, data roaming off
• HelloSIM line: switched on, set as the mobile data line, data roaming on
• Automatic data switching: off

With the home line's data roaming off, your carrier can't charge you for roaming data even if the phone briefly loses the eSIM signal. With data roaming on for the HelloSIM line, the eSIM can use the local networks it's designed for, at no extra cost, because the data is prepaid.

Which line should do what

Mobile data

Always the HelloSIM line while you're away. Everything that uses the internet then runs through the eSIM: maps, email, social media, messaging apps and app-based calls.

Calls and texts

Your home line. People ringing or texting your normal number still reach you. Keep in mind that your carrier sets the price of calls and texts abroad, and it can be significant, so check your current tariff before taking long calls. Many travellers reply with a message and move to a call over data instead.

WhatsApp, FaceTime and iMessage

WhatsApp is tied to your phone number, not to whichever SIM supplies the data, so it keeps working under your usual number while the data flows through the eSIM. FaceTime and iMessage also run over data; on a dual SIM iPhone you choose which number they use, so pick your usual one.

SMS codes from banks and services

This is the main reason to keep your home line switched on. One-time passcodes from banks, card issuers, airlines and work systems usually go by SMS to your registered number. If the home line is off, those codes won't arrive until you switch it back on.

Leave the home line on for calls and texts throughout the trip. Receiving texts abroad is often free, but carriers differ, so check your tariff once before you leave.

Avoiding surprise charges on your home line

Most dual SIM bill shocks come from one of three slips:

1. 1Data roaming left on for the home line. Turn it off before the plane lands.
2. 2Automatic data switching. On iPhone, "Allow Mobile Data Switching" lets the phone fall back to the other line's data when the signal is weak. Turn it off. Many Android phones have a similar automatic switching option in the SIM settings.
3. 3Long calls on the home number. Calls abroad are billed by your carrier, so check your current tariff and lean on data-based calls where you can.

Setting it up step by step

On iPhone

1. 1Install the eSIM at home over Wi-Fi: Settings → Mobile/Cellular → Add eSIM, then scan the QR code from your email.
2. 2When prompted, label the lines, for example "Home" and "Travel".
3. 3Set your home line as the default for calls and texts, and for iMessage and FaceTime.
4. 4On arrival, go to Settings → Mobile/Cellular → Mobile Data and choose the HelloSIM line.
5. 5Turn off "Allow Mobile Data Switching".
6. 6Open each line's settings: data roaming on for HelloSIM, off for your home line.

On Android

Wording varies by brand, but the steps are similar:

1. 1Add the eSIM under Settings → Network & internet → SIMs, or Connections → SIM manager on Samsung, and scan the QR code.
2. 2Rename the lines so they're easy to tell apart.
3. 3In the SIM preferences, set calls and SMS to your home line and mobile data to the HelloSIM line.
4. 4Turn roaming on for the HelloSIM line and off for your home line.

Before you go, and when you're back

Dual SIM only works if the phone supports eSIM and is carrier-unlocked, so check both before you buy; an "Add eSIM" option in Settings is a good first sign. Install the eSIM at home, since the plan's days only start once it connects at your destination.

When you're home again, set mobile data back to your home line and switch the HelloSIM line off. Your number never changed, so there's nothing else to undo.