What is Voice and SMS?

Voice and SMS mean placing and receiving ordinary telephone calls, and sending and receiving text messages tied to a phone number. Both are a different class of service from data, and the majority of travel eSIM plans sell data alone without including either. In practice that means your travel profile may have no usable telephone number at all, even while the internet on it works perfectly.

For most people this is not a problem, because contact while travelling now happens almost entirely inside apps — LINE, WhatsApp, a work meeting tool — all of which run over data. What does cause trouble is the verification message from a bank or another service, which still arrives as an SMS to your existing number. This page explains how to handle that without exposing yourself to home-network roaming charges you cannot control.

What data-only actually means

A data-only plan entitles you to internet access over a local network and nothing else. Everything that rides on the internet therefore behaves normally: maps, the web, email, ride hailing, hotel bookings, and calls placed inside apps. What does not work is dialling a number in the ordinary way, or receiving a text message on that profile, because no number was attached to it in the first place.

Some plans do come with a local number, and some include an allowance of minutes or messages, but not all of them and not in every country. The condition varies by provider and by plan, and the only reliable way to know is to read the details of the plan in front of you. If a plan page says nothing about voice or SMS, assume data-only and plan accordingly.

Why travel plans rarely include voice

The main reason is that habits changed. Travellers today rarely dial a telephone number abroad; they call through whichever app both parties already use. Selling data alone therefore serves most customers at a lower price, whereas traditional voice service carries additional cost and technical work for a feature comparatively few buyers actually use.

The second reason is that telephone numbers are a regulated resource, country by country. Issuing one to a short-term visitor involves far more process than granting access to data. As a result, plans that do include a number tend to come with specific conditions and to exist only in certain countries. If you genuinely need a number, check for it while choosing the plan rather than after installing the profile, because changing course later usually means buying again.

How calling through apps works

Calling through an app means sending your voice as data over the internet, without touching the operator's telephone system at all. As long as your data works you can call, wherever you are and wherever the other party is. The advantage is that no international call charge enters the picture. The limitation is that both sides need the same app and both need to be online.

In practice, agree with family or colleagues in advance on which app you will use, and tell them that your usual number may not take calls while you are away. That one sentence removes most of the first-day contact problems, and it stops people at home from ringing your normal number and running up charges of their own.

Keeping the home line for SMS without paying for data

The arrangement most travellers settle on is to keep the home line in the phone but switch off its mobile data and its data roaming completely. The line still attaches to a local network so it can take calls and receive texts, while nothing runs in the background on it. All internet then comes from the travel eSIM you have already paid for. The division of labour is simple and easy to verify in the settings.

One thing to be aware of is that receiving calls and texts abroad may carry charges at your home operator's rates, which differ from operator to operator and which we do not know. Ask yours before you travel how they treat incoming calls, outgoing calls, and incoming messages in the country you are visiting. Then you can decide whether to leave the home line on throughout or only when you are expecting a code.

1. 1Before leaving, list which services still verify you by SMSGo through banks, e-wallets, email accounts, and work logins, and note which ones send codes by text. Those are the only reason you need to carry the home line at all.
2. 2Switch to an app-based method where the service supports itMany services let an authenticator app replace text messages. Make the change while you are still at home, because the switch itself usually requires one final SMS to confirm.
3. 3Install the travel eSIM and make it the data lineRoute all internet through it so the home line never touches data for the whole trip.
4. 4Turn off mobile data and data roaming on the home lineThese are two separate switches, so turn both off. After that the home line has one job left: waiting for calls and messages.
5. 5Set the default line for outgoing callsA phone with several lines asks which one places calls. Setting it to a travel line with no number means calls simply fail, so choose the home line or set the phone to ask each time.
6. 6Test before you leave the houseHave somebody send you one text and place one app call to them. Doing both at home surfaces any problem while it is still trivial to fix.

Default lines for calls and messages

With two lines in the phone the system lets you decide which one places calls, which one sends messages, and which one carries data. All three are set separately, and this is where settings most often go wrong — for instance a travel line with no number set as the calling line, so every call fails and the plan gets blamed for what is only a line selection.

If your phone offers an option to ask before each call, turning it on for the trip is worth considering, because you see which line is about to be used every time. It costs a moment, which is a fair trade against accidentally dialling out on the wrong line while abroad.

Wi-Fi calling and voice technologies

Some handsets and some operators support Wi-Fi calling, which lets your home line place and receive calls over the internet instead of over a mobile network. It can be very useful abroad, but whether it is available depends on the handset, the operating system version, and the policy of the operator that issued your home line — including whether they allow it outside the country at all.

With that many variables, the direct route is to ask your home operator before departure whether it can be enabled, what it costs, and what needs configuring. Do not build a trip around the assumption that it will work. Treat it as a bonus if it does, and keep app calling as the plan you actually rely on.

Emergency calls

Emergency numbers differ from country to country, and how a handset treats an emergency call depends on the country, the network, and the device. It is not safe to assume in advance that yours will connect in every situation. What you can and should do is look up the emergency numbers for your destination before you go, and write them somewhere you can read without an internet connection.

Alongside the emergency numbers, note your embassy or consulate in that country, your accommodation address, and a contact number for someone at home, on paper or in an offline note. That set of details is most valuable in exactly the situation where the phone is unusable — the same situation in which you cannot look anything up online.

How much data app calls use

Voice calls in an app use less data than most people expect, especially compared with watching video or scrolling an image feed. Video calls use many times more, because moving pictures go along with the sound. The real figures depend on the app, the quality it selects for itself, and the state of the connection at the time, so there is no single number that applies everywhere.

When the allowance is running low, choose a voice call over a video call and enable any data-saver setting the app provides. If the conversation will be long, wait until you are on Wi-Fi at your accommodation. These habits stretch what is left considerably without buying more mid-trip, and if you want an estimate for the whole trip before you leave, our data calculator is a reasonable starting point.

Estimate the data this trip will need

When you would rather not carry two lines

Some people would rather switch the home line off entirely for peace of mind about charges. That works if you have already moved every verification away from SMS to an authenticator app or email, and told the people who need to reach you to use an app instead. The preparation has to happen before departure, because changing a verification method abroad usually stalls at the final step, which asks for one more text message.

A workable middle course is to switch the home line on only when you know a code is coming — while making a bank transaction, say — and off again afterwards. That limits the time it spends attached to a foreign network while preserving your ability to receive the messages that matter, without committing entirely to either extreme.

A voice and SMS checklist before you go

This list is meant to be worked through in one sitting before departure. Each item is quick, and together they cover nearly every reason people find themselves uncontactable on day one. If something does not go smoothly, fix it while you are still at home, where every one of these is far easier to resolve with a fully working home line.

• You know whether the plan you bought is data-only or includes a number
• Verifications that could be moved now use an authenticator app instead of SMS
• The home line has both mobile data and data roaming switched off
• The travel line carries data, and the calling line is set correctly
• Family and colleagues know which app to use to reach you
• The destination's emergency numbers are written down offline
• You tested one incoming SMS and one app call before leaving

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