What is a carrier lock?

A carrier lock, also called a network lock or SIM lock, is a restriction built into a phone so that it only works with SIMs from the operator that sold it. It is the single most common reason a travel eSIM installs correctly and then refuses to connect.

Why phones are locked at all

When an operator sells a phone cheaply with a contract, the discount is paid back over the months of that contract. The lock is what stops you taking the discount and leaving. Phones bought outright, from the manufacturer or a shop that is not an operator, are normally not locked.

The rules differ by country. In the United Kingdom, Ofcom banned the sale of locked phones in December 2021, so a phone bought there since then should be unlocked. Elsewhere the usual arrangement is that the operator must unlock free of charge once the phone is paid off, but the conditions vary enough that the only reliable answer comes from your own operator.

How it shows up with an eSIM

This is the confusing part, because a lock does not usually stop the installation.

The profile downloads, the line appears in Settings, everything looks right. Then there is no service, or the phone sits on "Searching", or it registers for a moment and drops. From the outside it looks like a broken eSIM, and people spend an hour reinstalling a profile that was never the problem. Remember that deleting and reinstalling usually will not work twice, so this is an expensive mistake.

On some phones the signs are clearer: the option to add a second line is missing, or Settings shows a message naming the operator.

How to check

The quickest test is a SIM you already have from another operator, physical or eSIM. If it works, the phone is unlocked.

Without one:

• iPhone: Settings, General, About, then look for Carrier Lock. "No SIM restrictions" means unlocked.
• Android: Settings, About phone, SIM status or Network. The wording varies by manufacturer, and some do not show it at all.

If nothing in Settings says, ask the operator with the IMEI in hand. Avoid the paid unlocking services: your operator does it for free when you qualify, and the services that promise it otherwise are usually selling you something you already have the right to.

Quick answers

Will a travel eSIM work on a locked phone?

Usually not. The profile often installs and then cannot register on the network, which looks like a faulty eSIM but is not.

How do I know if my phone is locked?

On iPhone, Settings, General, About, under Carrier Lock. On Android it depends on the manufacturer. The reliable test is any SIM from a different operator.

Is unlocking free?

From your own operator, normally yes once the phone is paid off, though the conditions differ by country. Phones sold in the UK since December 2021 cannot be locked at all.

Does unlocking erase my phone?

No. It is a change to how the phone accepts SIMs, not to what is stored on it. Your data stays where it is.