Data-Only eSIM: Calls, WhatsApp and Your Phone Number

The most common question about travel eSIMs isn't about data at all. It is about the phone number: will it change, will WhatsApp still work, and will the bank's text message still arrive? The answer depends on one phrase you will see on most travel eSIMs, including HelloSIM's: data-only. Once you know what that means, setting up your phone so that everything keeps working is straightforward.

What "data-only" means

A data-only eSIM gives your phone a mobile internet connection and nothing else. It comes with no local phone number, so it cannot make or receive regular phone calls or SMS text messages.

That sounds like a limitation, but in practice it rarely is, for two reasons:

• Almost everything you do on a phone abroad runs over the internet: maps, email, browsing, ride and booking apps, social media, and most calls and messages.
• Your regular SIM doesn't go anywhere. A data-only eSIM is added as a second line, so your usual number remains active alongside it.

In other words, you are not swapping your phone number for a travel one. You are adding a data connection to the number you already have.

Calls and messages over the internet

With a data-only eSIM providing your connection, calls and messages work through internet-based apps exactly as they do on Wi-Fi at home:

• WhatsApp, Telegram and Viber for messages, voice calls and video calls.
• FaceTime and iMessage between Apple devices.
• Video meeting apps for work calls.

The person you are calling doesn't need to do anything differently. They see your usual account and answer as normal. Voice calls use relatively little data, while video calls use considerably more, so if you plan regular video calls home, choose a plan size that allows for it. A handy rule of thumb: light use is roughly 1 GB a week, regular use 3–5 GB, and heavy use including frequent video 10 GB or more.

What a data-only eSIM can't do is ring a traditional phone number through your phone's own dialler. For that, you would use your home SIM, or a calling app that supports calls to phone numbers.

WhatsApp, iMessage and your number

WhatsApp is tied to your usual phone number, and a data-only eSIM changes nothing about that. WhatsApp doesn't care which line supplies the internet; it simply uses whatever connection is available. Your chats, groups and contacts stay exactly as they are, and you don't need to register again.

iMessage and FaceTime on iPhone work the same way. When you add an eSIM, the iPhone may ask which line to use for iMessage and FaceTime. Choose your usual number, and messages will continue to come from and go to that number while the eSIM provides the data.

Keeping your number for SMS codes

The one thing internet apps can't replace is the traditional SMS. Banks, card issuers, airlines and many apps send one-time verification codes by text to your usual number, and you may need one at an inconvenient moment, such as when paying for something online abroad.

That's why you should keep your home SIM switched on while you travel:

• Leave the home line active so it can receive calls and texts.
• Keep data roaming off on the home line, so it doesn't use your home operator's data.
• Check your home tariff for what incoming calls and texts cost abroad, as this varies by operator and destination.

Because a data-only eSIM sits alongside your own SIM rather than replacing it, those codes keep arriving where you expect them.

Setting up dual SIM

Most eSIM phones can use two lines at once. The aim is to give each line one clear job: home SIM for calls and texts, travel eSIM for data.

On iPhone, once the eSIM is installed (Settings → Mobile Data or Cellular → Add eSIM):

1. 1Give the lines clear labels, such as "Home" and "Travel".
2. 2Set your default line for calls and texts to your home number.
3. 3Set Mobile Data to the travel eSIM.
4. 4On arrival, turn on Data Roaming for the travel eSIM line, and turn it off for the home line.
5. 5Consider turning off "Allow Mobile Data Switching", so the phone doesn't try to fall back to your home line's data.

On Android, once the eSIM is added (Network & internet → SIMs on Pixel-style menus, Connections → SIM manager on Samsung):

1. 1Set the preferred SIM for calls and SMS to your home SIM.
2. 2Set the preferred SIM for mobile data to the travel eSIM.
3. 3Enable roaming on the eSIM line and leave it off on the home line. Menu names vary by brand.

Roaming has to be enabled on the eSIM line or it won't connect at your destination; with prepaid data this adds no charge. The plan's days begin with that first connection abroad, not on the day you install it.

Avoiding surprise charges on your home line

Dual SIM is safe as long as each line stays in its lane. The most common mistake is leaving data roaming on for the home SIM, which lets apps quietly use your home operator's data abroad. Home operators frequently bill that by the day or by the megabyte, depending on the tariff, so check before you go.

Answering calls on your home number abroad can also be charged by your operator. If you would rather not risk it, ask friends and family to call you on WhatsApp or FaceTime instead, which uses the eSIM's data.

When data-only isn't the right fit

A data-only eSIM covers most travellers, but not every situation. If you need a local phone number, for instance so a local landlord, employer or delivery service can call or text you on a number in that country, a data-only eSIM won't provide one. Your handset must also be eSIM-capable and carrier-unlocked.

For everything else, it does the job. HelloSIM plans cover 190+ destinations, from single countries to regions and a Global plan, and if you need more data, you can top up the existing eSIM from your account, the app or the Check / Top up page. Questions about your set-up can go to [email protected] or to the live chat inside the HelloSIM app.