Note · · 4 min
Data-only SIMs and messaging apps: what works, and keeping your home number for bank codes
A travel eSIM gives a phone data but not a new number. Once that is clear, most of what works and what does not follows from it.
Every PERDIEM plan is data only. The eSIM connects the phone to mobile internet in the destination, but it has no phone number attached. It cannot make or receive ordinary calls, and it cannot send or receive text messages.
That sounds like a limitation, and in one sense it is. But it is also how most families already talk to each other. So much of it happens in apps that only need a data connection.
What works over data
Messaging and calling apps that run over the internet work as they do at home. WhatsApp, Signal, Telegram, iMessage and FaceTime all use data rather than the phone network. Your contacts see the same name and number they always do, because these apps are tied to your account, not to whichever line is carrying the data.
WhatsApp, for example, is registered to your home number, but it does not need that line to be carrying data to keep working. Avoid reinstalling it or moving it to another phone while you are away. That can prompt it to verify your number again by text, which brings you back to the home line.
What does not
Ordinary calls and texts to and from your home number still go through your home network. If someone rings your normal number while you are abroad, the call reaches your home line, not the travel eSIM. Whether that costs anything depends on your contract and where you are.
Texts sent to your number, including verification codes, also arrive on the home line. That is the part to plan for.
Keep the home line switched on
Banks, card providers and many online accounts send one-time codes by text. If the home line is removed or switched off, those codes will not arrive. A card payment or a login that needs one can then fail at the worst possible moment.
So keep the home line installed and switched on, alongside the travel eSIM. Phones that support eSIM can generally run two lines at once. Receiving texts abroad is free or cheap on many contracts, but check yours rather than assume. Some banking apps can approve a payment inside the app instead of by text. If yours offers that, set it up before you travel.
The settings that matter
The aim is simple. The travel eSIM carries data. The home line handles calls and texts. The home line uses no data abroad.
Set the travel eSIM as the line for mobile data, with data roaming turned on for that line. On the home line, turn data roaming off. That stops the home line using data abroad, even if the phone briefly switches to it. On iPhone there is also a setting that lets mobile data switch between lines; turning it off keeps data on the travel line. Many Android phones have something similar in their SIM or dual SIM settings.
Some phones let you choose a default line for calls and for texts separately. Set both to the home line. Menu names differ between models and software versions, so if a label here does not match your phone, look for the nearest equivalent rather than a word-for-word match.
Wifi calling and other edges
Some home networks offer wifi calling, which can carry calls on your home number over an internet connection. Whether it works abroad, whether it works over another line's data, and whether it is charged all depend on your network. Ask them before relying on it.
If a teenager or a grandparent needs to be reachable on their usual number, for a school, a club or a doctor's surgery, the same rule applies to them. Their number still works, through their home network, on the same terms as before. The travel eSIM only takes over the data.