I have a smartphone bought at home (Europe) and I changed providers during the time I've had it. This meant I went to my new provider, asked to become a customer. They gave me a new SIM card (with number transfer, so I kept my old number). I put it into my phone, they activated it, it worked. Both old and new providers operate in the same country.

At that time, I hadn't heard about locked and unlocked phones. Now that I'm planning on a trip outside of Europe (to the US) and want to buy a SIM card there, I'm reading everywhere that your phone has to be unlocked or it won't work with another carrier.

Does my previous experience mean my phone is already unlocked? Or is this unlocking something specifically for changing countries?

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    Have you asked your current provider? – Traveller Apr 30 '18 at 8:30
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    How did you bought your smartphone? If it was not a part of your mobile contract and you just bought it (which I presume) it was never locked. – Neusser Apr 30 '18 at 8:49
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    I'm voting to close this question as off-topic because it is about mobile phones, not travel. The fact that the asker wants to use a foreign SIM card makes no material difference to the question -- the answer would be the same if they wanted to buy a new SIM in their own country. – David Richerby Apr 30 '18 at 10:33
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    @DavidRicherby This question could be about travel as for some phones, foreign SIM card do make a difference. See my answer. – DCTLib Apr 30 '18 at 10:49
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    @David Richerby I already know an own-country-SIM card would pose no problem. I wanted to know if abroad-SIM cards have a separate locking mechanism. – Hekx Apr 30 '18 at 11:11

Is my European smartphone already unlocked?

Yes. Most likely.

The only commonplace form of locking that I am aware of that is used by vendors of phones in Europe is locking the handset to SIMs issued by a specific phone-network when that network subsidises the initial cost of the phone. When purchasing a phone you usually have a choice of monthly-tariff, pay-as-you-go (UK term) or SIM-free. The SIM-free option is always unlocked in my experience.

Note that there are also various "locks" that the end-user can enable on the phone hardware and/or separately in the SIM - basically a kind of password. These are not relevant.

I changed providers

When you change network providers in the EU (or at least in the UK), the phone must be in an unlocked state. If it was previously locked, you typically pay the existing provider an unlocking fee - after which the phone can be used with any provider's SIM.

You might not need to unlock the phone, if you change between providers that use the same underlying network, for example when there is one or more mobile virtual network operators (MVNOs) using the same underlying network. E.g. changing SIM from one provided by a network operator to an MVNO using their network or between two MVNOs using the same network.

I've never had any problem with a phone bought in the UK used in other parts of the planet. There can be problems with frequencies supported - in the early days you paid a premium for tri-band or quad-band GSM phones that would work in the USA (there were basically two types of phone, ones that worked worldwide except the USA and ones that worked in the USA). Nowadays the situation is far more complicated. I just wing it, I figure I can always buy a cheap phone at the other end if things don't work out.

  • Sometimes you can use locked phones on other networks if they are an MVNO using the same underlying network. For example, I bought an O2 locked phone and had no problem using it with a GiffGaff SIM. – Robin Salih Apr 30 '18 at 15:36

There are two types of locks:

  • A "SIM lock" that restricts which SIM cards from which provider you can use.
  • A "Region lock" that restricts in which regions your phone can be (initially) used.

For the former, you should check with your provider. If you once changed to a different company, then most likely you do not have a SIM lock. (See also the answer by Sebastiaan van den Broek)

The second type of lock is cell phone manufacturer-specific. For example, Samsung build such a lock into their phone such that you need to use it with a local SIM card in the geographic region stated on the phone cardboard box for at least 5 minutes of talk time before it can be used in another region. Shouldn't be a problem for you either.

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    I would also add that in different part of the world different frequencies are used. While GSM is universal, if you want 4G in the US, depending on the carrier, an EU phone might or might not be compatible. – Vladimir Cravero Apr 30 '18 at 13:00
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    There is also hardware compatibility to look at, too - phones don't support all mobile telephone network bands. At one time it was quite likely phones would work in one region but not another, but nowadays it's very probable that at least minimum compatibility will exist. Still, just because a phone supports LTE at home does not guarantee it will in a foreign country. – Jim MacKenzie Apr 30 '18 at 13:21

You should take at your country’s legislation at for example https://en.wikipedia.org/wiki/SIM_lock and then if necessary check it with your provider.

Europe or the EU does not have a law against this such as for example Singapore, but in my experience it’s not a common practice to sell locked phones anymore. Still best to find out before you need the phone elsewhere though.

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