Embedded SIMs have changed international phone use more than any other recent development, and the practical detail is scattered and inconsistent enough to be worth setting out.
What actually changed
Previously, getting a local connection abroad meant finding a shop, providing identification in some countries, physically swapping a card, and keeping the original somewhere safe.
Now it is a purchase and a scan, done before departure, active on arrival.
The larger change is that a phone can hold several profiles simultaneously and switch between them, so you keep your usual number for calls and messages while using local data.
That dual arrangement is the main practical benefit and it is what makes the whole thing worthwhile.
The categories of provider
Three, with different economics.
Your existing operator's roaming package, which is the most convenient and generally the most expensive, though the gap has narrowed and some are now competitive.
Travel-focused providers selling data plans for specific countries or regions. These are typically cheapest for data and generally provide data only, with no local number.
Local operators in the destination country, which offer the best rates and full service including a local number, and which sometimes require in-country purchase or identification.
For most short trips the travel provider is the sensible choice. For longer stays a local operator is substantially better value.
What to check before buying
Whether your device is compatible and, critically, whether it is carrier-locked, since a locked device may refuse other profiles.
Whether the plan includes a phone number, which many data plans do not, meaning no calls or text messages on that profile.
Which networks it actually uses in the destination, since travel providers resell capacity and coverage differs between host networks, particularly outside cities.
Whether tethering is permitted, which is frequently restricted on cheaper plans and is a common reason for disappointment.
And the validity period, which usually starts on activation rather than on purchase, so buying early is safe if you activate late.
The practical setup
What I do now, having got it wrong twice.
Install the profile before leaving, while on a reliable connection, but do not activate it. Installation requires internet access, which is exactly what you will not have on arrival.
That is the single most common failure and it is entirely avoidable.
Set the home profile to allow calls and messages but disable its data, and set the travel profile as the data line. This keeps you reachable on your usual number without incurring roaming data charges.
Check that messages requiring a network connection still work, since some services behave oddly with multiple profiles.
And save the provider's support details somewhere reachable without the connection you are trying to fix.
The things that go wrong
From experience and from watching others.
Deleting a profile is usually irreversible. Removing one to make space and expecting to reinstall it is a mistake, since many providers issue single-use activation codes.
Profile limits, since devices support a finite number of stored profiles, and heavy travellers hit that limit.
Verification messages sent to your home number, which arrive normally if the home profile is active and do not if you have disabled it entirely.
And devices that appear to support the technology while the operator does not, which remains true in several markets.
The regulatory angle
Worth knowing because it varies.
Several countries require identity registration for any mobile connection, and this applies to embedded profiles as well as physical cards. Providers handle it during purchase, and it can require documentation.
Some countries restrict or prohibit foreign profiles entirely.
And the transferability of a profile between devices depends on the provider, which matters if a phone is lost or replaced mid-trip. Some allow a straightforward transfer and some do not, which is worth establishing before you need it.
What I would tell somebody
Install before departure, activate on arrival.
Keep your home number active for messages and disable its data.
For anything longer than a fortnight, buy locally on arrival instead.
And check the tethering position specifically if you intend to use a laptop, since that is where the restriction bites and where people discover it at the worst moment.
Business and multiple numbers
A use beyond travel that is worth knowing about.
Holding a work profile and a personal profile on one device removes the second phone, with separate numbers and separate billing.
The caveat is that a work profile provisioned by an employer may come with device management attached, which can grant capabilities over the whole device rather than the profile.
Worth asking what management is applied before installing anything an employer provides, since the answer varies and is not always volunteered.
Losing the phone
The scenario worth thinking about in advance, since the recovery differs from a physical card.
A physical card can be moved to a borrowed handset immediately. An embedded profile generally cannot without contacting the provider.
Which means losing a phone abroad can mean losing the number used for authentication codes at exactly the moment you need to prove who you are.
Worth having at least one authentication method that does not depend on that number, and knowing your provider's replacement process before travelling rather than researching it from a hotel.