Buying a used phone is a gamble. You're scrolling through Facebook Marketplace or Swappa, you see a "mint condition" iPhone 15 Pro, and the price is almost too good to be true. You meet the seller at a coffee shop, check for scratches, and peek at the battery health. It looks great. But then you get home, pop in your SIM card, and—nothing. The dreaded "SIM Not Supported" message crawls across the screen. You’ve just bought a paperweight. Learning how to know if iPhone is unlocked isn't just a technical curiosity; it’s financial self-defense in a world where carriers love to keep their hardware on a short leash.
Most people think a phone is "unlocked" if it doesn't have a passcode. That's a massive mistake. We're talking about the network lock—the digital handcuffs that tether a device to AT&T, Verizon, or T-Mobile. If your device is locked, it won't work with any other carrier. Period.
The Settings App Secret
The easiest way to check is buried right in your software. Honestly, Apple made this much simpler in recent years, but hardly anyone knows where to look. Grab the phone. Open Settings. Tap General, then tap About. You're going to scroll down until you see a field labeled Carrier Lock.
If it says No SIM restrictions, you’re golden. You can take that phone to any carrier in the world, from a local shop in London to a prepaid booth in Tokyo. But if it says anything else—like "SIM Locked"—you're stuck. This is the gold standard for a quick check. It’s pulling data directly from the device's activation policy. However, I've seen cases where this field is a bit glitchy on older versions of iOS (specifically anything before iOS 14), so it isn't always 100% foolproof if the phone hasn't touched a Wi-Fi network in a while.
Why the SIM Card Swap is Still King
Software can lie. Hardware doesn't. If you want to be absolutely, undeniably sure about how to know if iPhone is unlocked, you need two SIM cards from two different networks.
Let's say the phone is supposedly on Verizon. Borrow a friend's T-Mobile SIM. Power the iPhone down. Pop the tray with a paperclip. Swap the cards. Turn it back on. If the phone catches a signal and shows the carrier name in the top corner, it’s unlocked. If a screen pops up saying "Activation Required" or "SIM Not Supported," the phone is locked. It’s a bit of a hassle to carry a spare SIM, but it's the only way to test the physical modem's behavior in real-time.
Remember that with the newer iPhones (14, 15, and 16 series in the US), there is no physical SIM tray. Everything is eSIM. This makes the "swap test" a lot harder for the average person standing on a sidewalk during a Craigslist deal. You’d have to try and trigger an eSIM transfer, which is a giant pain. In those cases, you’re going to rely heavily on the Settings menu and IMEI checkers.
The IMEI Deep Dive
Every iPhone has a digital fingerprint called an IMEI (International Mobile Equipment Identity). It’s a 15-digit code that tells the story of the phone's life. To find it, dial *#06# on the keypad or look in Settings > General > About.
You can take this number to various online portals. Be careful, though. A lot of "Free IMEI Check" sites are just fishing for your data or trying to upsell you on sketchy unlocking services. Use a reputable one like SickW or even the carrier's own bring-your-own-device (BYOD) pages. T-Mobile and Verizon have pages where you can type in an IMEI to see if it’s compatible. If the Verizon page says "This device is not compatible" but it’s an iPhone 13, it’s probably because it’s locked to another network.
The Difference Between "Locked" and "Blacklisted"
Here is where it gets messy. A phone can be "unlocked" but still totally useless.
Imagine a phone was bought on a payment plan and the original owner just stopped paying. Or worse, it was reported stolen. The carrier puts that IMEI on a "blacklist." Even if the phone is technically unlocked and could support any SIM, the network towers will see that ID and refuse to connect. This is why you should always check the GSMA blacklist status. If a seller is acting twitchy when you ask for the IMEI, walk away. There is no "fix" for a blacklisted phone that doesn't involve some very shady, and often illegal, software bypasses.
Why Carriers Lock Phones Anyway
It’s all about the money. Carriers subsidize the cost of these $1,000 devices. They give you a "free" iPhone 16, but they make that money back over a 36-month contract. To ensure you don't take their expensive hardware and run over to a cheaper competitor, they lock the software.
Under the Unlocking Consumer Choice and Wireless Competition Act, carriers are actually required to unlock your phone once you’ve paid it off. But they won't do it automatically. You usually have to beg them. AT&T has a specific web portal for this. Verizon is the "nice" one; they automatically unlock most devices after 60 days of active service due to an old agreement they made with the FCC regarding 700MHz spectrum.
Real-World Scenario: The International Traveler
I once had a friend move to France with what he thought was an unlocked iPhone 12. He had paid it off months prior. He landed in Paris, bought a local Orange SIM, and... nothing. It turns out that while he had paid the balance, he never officially requested the unlock through the AT&T portal.
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He was stuck in a foreign country without a working phone because he didn't check the "Carrier Lock" status in his settings before leaving. Don't be that guy. If you’re planning to travel, check your status at least a week before you head to the airport. If it says "SIM Locked," you have time to call your carrier and scream at them until they process the request. Usually, once they "push" the unlock, you just need to connect to Wi-Fi for the phone to talk to Apple's servers and update its status.
Dealing with "Reseller Flex Policy"
This is a weird one that even some pros miss. If you buy an iPhone from a big-box retailer like Best Buy or Target, it might come with something called a "Reseller Flex Policy." These phones look unlocked in the box. They aren't tied to any carrier.
However, the moment you put the first SIM card into the phone, it "slugs" to that carrier. If you put a Sprint SIM in first, that "unlocked" phone is now a Sprint phone. Permanently. Well, until you meet Sprint's (now T-Mobile's) requirements for unlocking. If you’re buying a "new in box" iPhone from a third party, be very wary of this. The best iPhones are the ones bought directly from Apple (the "Sim-Free" models) because they never lock, regardless of which SIM goes in first.
How to Handle a Locked Phone You Already Own
So you checked, and it’s locked. Now what?
- Check your contract. If the phone is paid off, the carrier is legally obligated to unlock it.
- Contact the original carrier. You’ll need the account holder's info if it’s not yours. This is why buying locked phones from strangers is a nightmare; the carrier won't talk to you because you aren't the original customer.
- Third-party services. Use these as a last resort. They essentially pay someone on the "inside" or use automated portals to request the unlock. They are hit or miss and can be expensive.
- The "R-SIM" or "Turbo SIM" hack. You might see little thin stickers that go on your SIM card. These "trick" the iPhone into thinking it’s on the right network. They are buggy, they drain battery, and they often break whenever you update iOS. Avoid them.
Actionable Next Steps
If you are currently holding an iPhone and need to know its status, follow this exact sequence:
- Go to Settings > General > About > Carrier Lock. If it says "No SIM restrictions," stop. You are done. It is unlocked.
- If it says "SIM Locked," identify which carrier it is tied to (usually listed under "Carrier" in that same menu).
- Check the IMEI on a site like
SNDeepInfooriFreeIMEIto see if it’s clean or blacklisted. - If you are buying the phone, ask the seller to show you the "No SIM restrictions" screen in person. If they can't or won't, assume the phone is locked and adjust the price you're willing to pay—or just walk away.
- For phones already owned, call your carrier’s "International Travel" or "Account" department. Tell them you’re traveling and need the device unlocked. If the phone is paid off, they usually handle it within 24–48 hours.
Once the carrier confirms the unlock, you don't usually need a code (unlike Android phones). You just need to insert a SIM from a different carrier or simply restart the phone while connected to a strong Wi-Fi signal. The phone will "call home" to Apple, realize its status has changed, and unlock itself silently in the background. It's a seamless process when it works, but a bureaucratic nightmare when it doesn't.
Don't take the seller's word for it. Don't assume "paid off" means "unlocked." Check the settings, verify the IMEI, and if possible, do a physical SIM swap. That is the only way to be certain.