What is an eSIM and should I switch to one?

What changes when the SIM becomes software, where it is genuinely better, and the two situations where a plastic SIM is still easier.

Difficulty: beginner
Time: 15 min
Read: 3 min

Short answer

An eSIM is a SIM built into the phone and activated by scanning a code, so there is no card to post or swap. It is faster to set up, lets you hold several numbers at once, and is much better for travel. The trade-off is that moving it to another handset needs the network's involvement rather than a paperclip.

Most recent phones support eSIM, and some no longer have a card slot at all. It is not a change you need to make, but it removes several long-standing annoyances if you travel or want a second number.

Step by step

Check the phone supports it.Look in the phone's settings for a mobile or cellular section that offers to add a data plan or eSIM. If that option exists, it is supported.
Ask the network to issue one.Most UK networks will convert an existing plastic SIM to an eSIM free, either in an app or by request. They send a QR code or an activation link.
Activate it somewhere with wifi.Scanning the code needs a connection, and the old SIM often deactivates during the process. Doing it at home with wifi avoids being stranded with neither working.
Understand the dual-SIM advantage.Most eSIM phones can hold multiple profiles and run two at once — a personal and a work number, or a home number plus a local plan abroad, with control over which one makes calls and which carries data.
Use it for travel rather than roaming.A local or regional travel eSIM bought before you fly is often far cheaper than roaming, arrives instantly, and leaves your usual number active for calls and texts.
Know what changes when you replace the handset.There is no card to move. Newer phones can transfer an eSIM between handsets directly; otherwise the network reissues it, which is quick but requires them to be open.
Keep a record of the activation details.Store the network's account details and support number somewhere other than the phone itself, because reactivating usually needs you to sign in to something.
Think about security.An eSIM cannot be pulled out of a stolen phone, which is a genuine advantage. It does not protect against SIM swap fraud, where someone persuades the network to reissue your number — an authenticator app rather than SMS codes is what helps there.

Tips

Do not delete an eSIM profile from a phone you are getting rid of until the replacement is working — deleting it can require the network to reissue.
Travel eSIMs are usually data only. Keep your normal SIM active for calls and texts, with roaming data turned off.
If you swap between two handsets often, a plastic SIM is still genuinely more convenient.

Common mistakes

Deleting the eSIM before the new phone is set up — It cannot simply be reinserted. You are dependent on the network reissuing it, which may not be immediate.
Activating a travel eSIM at the airport on arrival — Activation needs an internet connection. Buy and install before you fly, then switch it on when you land.

If it doesn't work

QR code will not scan

Cause: Poor lighting, or the code has already been used — Fix: Ask the network for the manual activation details, which most will provide as text you can type in. A used code cannot be reused.

Two SIMs active but the wrong one is used for data

Cause: Default line settings — Fix: In the phone's mobile settings there is a choice of which line handles data, calls and texts. Set data to the cheaper line.

No service after activating

Cause: The profile is installed but not enabled, or the old SIM is still selected — Fix: Check the eSIM line is turned on in settings, then restart the phone. Give it a few minutes to register.

Questions people ask

Is an eSIM safer than a plastic SIM?

Against theft, yes — it cannot be removed from the handset. Against SIM swap fraud it makes no difference, because that attack targets the network account rather than the card.

Can I go back to a physical SIM?

Usually yes, if the phone has a slot. The network posts a card and deactivates the eSIM. Some newer phones have no slot at all, so check first.