eSIM + WiFi calling: Stay connected everywhere without the fuss

Dominik Rüttiger 4 min read

Sep 3, 2023

I still remember buying discount cards for using public telephone booths when traveling. My, how the world has changed! Now, I feel almost the same way about buying physical local SIM cards.

Many people do not know that nowadays, you can buy local eSIM cards directly from your phone. Some providers even allow you to do this without an internet connection. Combined with WiFi calling, you will never lose connection with home and save a lot of time and money.

Buy eSIM via app

Apple made using eSIMs possible and popular with iPhone XS and XR in 2018. The major mobile telecommunications operators’ support for eSIM has been frustratingly slow. It gained big momentum, now, that the US version of the iPhone 14 in 2022 does not even support physical SIM cards any more.

But for quite some time, there has been a new generation of companies which will provide you with eSIMs right from your phone. Some companies I can recommend personally are:

Usually they will give you data-only SIM cards, which do not require a complicated identification process.

Typical flavors are local, regional, global eSIMs:

local: use within a specific country (e.g. Japan)
regional: use within a specific region (e.g. Asia)
global: use in all countries the provider covers (e.g. 84 countries)

It’s common to buy a one-time monthly plan with a certain amount of data. For Japan, for example, you can get 3 GB for as low as $8 and 10 GB for $18.

Step-by-step

The safest option is to exactly follow the instructions within the app you choose. But the basic steps are always the same:

Download the app
Choose a plan
Install the eSIM
Adjust phone settings

It makes sense to double check the phone settings for cellular, especially if you want to keep your home SIM card activated. On iPhone, they can be found in the Settings app under Cellular:

Cellular Data: Choose the SIM card you want to use for data, which is usually the eSIM you just installed.
Default Voice Line: If you bought a data-only eSIM, this usually is your home SIM card.
Cellular Plans: Switch off roaming for your home SIM card.

Warning: If you want to be 100 % safe to not spend any money on your home SIM card, either remove or deactivate it.

WiFi calling

Imagine, you step off your airplane, keep Airplane Mode switched on and your home SIM installed. Most people do not know, that you can keep using your home number by connecting to any WiFi.

This is made possible by WiFi calling and is supported by most providers. From your provider’s perspective, there is no difference if you use your phone at home or via WiFi calling abroad.

Important: Within European Union there is a special roaming agreement, that allows you to make phone calls in the country you are visiting for the same conditions as in the home country. If you have a flatrate, it’s even for free.

If you want to use this advantage, you have to switch off WiFi calling.

Bonus: WiFi calling without WiFi

To use Wifi calling, you usually need a WiFi connection, of course. So if you wanted to use it on the move, you would need a mobile router. But there is a surprising exception: if your home SIM card has a spending cap, you can combine it with a local data eSIM and it will magically make “WiFi calling” through the local data eSIM.

Because of the spending cap, the home SIM card will not log in to the foreign country’s network and will instead use the mobile data of the local data eSIM.

Not all providers offer plans with a spending cap. But plans that were originally aimed at children usually have this feature. In Germany, for example, Fraenk guarantees that you cannot spend more than your fixed monthly fee.

Bonus: Release your phone number from SIM cards

If you want to go one step further: Get a phone number that is not tied to a SIM card. You can use a SIP trunk from a local provider and use a standard VoIP client app on your phone. Even easier are apps like satellite, that combine both.

That way, you can use your phone number with any data network. So any WiFi or data SIM will work.