Best answer: If you didn't buy a phone that was advertised as unlocked the best way to make sure is to try a SIM card from a different carrier. If you don't have one, you can probably get a carrier to help out.

Amazon: Samsung Galaxy Note 9 ($999)

Why unlocked?

You've probably heard a lot of talk about using MVNO carriers as a way to find a cheaper alternative for service. It's something that's gaining popularity and while it isn't exactly mainstream just yet, it's getting there. We think that's great because having even more choices can't be a bad thing. But in most cases, before you can try any other service provider, you'll need to have a SIM-unlocked phone. That means you can use a SIM card from any company and as long as the hardware is compatible with the network, it just works.

While some of us already know if our phones are unlocked or how to check, here's what you need to know if you are looking for a little help.

Where did you buy it, and how?

In the U.S., Verizon is the only carrier that sells most of its smartphones unlocked. What we mean here is that if you walk into a Verizon store or use its website and buy a phone made for Verizon with the branding on it, it's probably going to be SIM unlocked. Note that this doesn't mean you should buy a Verizon branded phone to use on a different network because SIM unlocked doesn't mean fully compatible. We just mean that Verizon is OK with you putting another SIM in the phone and letting the hardware try to connect to a different network.

The other three networks, as well as Best Buy or other third-party carrier resellers, are not as reliable when it comes to selling unlocked phones. Some phones are, some aren't — but every one of them can be unlocked, because that's the law.

If you bought your phone from Amazon or B&H or another online retailer, it told you in the listing if it was unlocked. If you don't remember, a quick call or email to customer service will help you find a copy of the listing to double check. Of course, if you bought your phone directly from the manufacturer and if it was listed as unlocked, it will be. All phones sold directly from Google and Apple (if paid in full at time of purchase) are unlocked, and many phones from other manufacturers are sold directly and SIM unlocked, too.

For the rest of the phones out there, there's really only one fool-proof way to check — try it.

Use a SIM card from a different carrier

You'll see websites that claim you can check if your phone is unlocked online. While that might be true, these services cost money and are often incorrect. I'll come right out and say it — don't bother.

You can call your carrier or the carrier or MVNO you're thinking of switching to. Companies keep a database of IMEI numbers that says which phones are compatible, unlocked, or blacklisted. You might not have any luck here, though, because the person answering the phone might not be able to give you that information — they either don't have access to it or they aren't allowed to tell you over the phone. It's worth a try if you don't have access to a SIM card from a different company, though.

If you do have access to a SIM card from a different carrier, checking is pretty simple. And it doesn't have to be a SIM card connected to an active account — the phone will try to initiate a connection with any SIM card in place.

  • Make a phone call using the current SIM card if possible. This is to check that the phone is working properly. Call your mom and tell her hello; she'll appreciate it.
  • Shut off the phone and remove the SIM card. Look in the manual or online if you're not sure how to do this, and if you need a SIM card removal tool, a paperclip works fine.
  • Put the different SIM card in the phone and power it back on.
  • If you're greeted with a dialog box telling you to enter an unlock code, your phone is SIM locked to the carrier it was originally purchased from.
  • If you don't see this, check that it says you have service if you used a valid SIM card. If you do, your phone is probably unlocked. Try making another phone call. Mom won't mind two calls on the same day.

If you can't call using the different SIM card, you'll probably get a recorded message with some error code. You can jot down the code and check online to see why the call can't be completed so you know if it's because of a SIM lock or because of incompatible hardware.

You can also carry your phone into a carrier store and tell them you're thinking of switching carriers and want to check if it's unlocked. Your current carrier should help you, but if not, try an AT&T or T-Mobile store even if you're not going to switch to AT&T or T-Mobile. Don't feel bad about telling a little white lie to a carrier — they tell them to us all of the time. They should be able to help you put in a SIM card and check.

If your phone is SIM-locked, don't fret. As mentioned, a carrier has to unlock a phone unless you owe money on it according to U.S. law. Give them a call and they will help you.

When you don't need a SIM-unlocked phone

At the top of this article, we said in most cases you do need a SIM-unlocked phone to try another carrier. That's true, but there is one popular use-case where it doesn't matter: using a T-Mobile branded phone on an MVNO using T-Mobile's network or an AT&T branded phone on a MVNO that uses AT&T's network..

AT&T and T-Mobile actively assist resellers, and they don't require a reseller (that's what an MVNO is) to require you to have an unlocked phone to connect. If your phone says T-Mobile on it or on the box, it will work on most MVNOs that use T-Mobile's network. The same goes for a phone from AT&T. And there are a lot of them.

Our pick

Samsung Galaxy Note 9

The best unlocked phone you can buy

The Galaxy Note 9 is one of the most versatile and powerful phones on the market. You get top-end specs across the board, plus all of the hardware features you expect. Just about anyone looking for a high-end phone will love using the Note 9.

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