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What are unlocked phones?

What are unlocked phones

What you need to know about unlocked phones.

Unlocked phones are cell phones without SIM lock that can be used with any GSM carrier. Simply slip your SIM card into your new phone and you are ready to go – make phone calls, send text messages and surf internet.

Due to their popularity, unlocked phones usually refer to GSM phones supporting SIM cards, for example AT&T and T-Mobile.

Lately meaning of the term unlocked phones has been expanded beyond GSM technology reaching CDMA devices. For instance the unlocked Verizon and unlocked Sprint phones can be activated and used with GSM carriers, such as AT&T or T-Mobile.

However, unlocked GSM phones cannot be used with Verizon or Sprint service. You need to pay attention before purchasing an unlocked phone. Confused?

Confused about locked and unlocked phones?

Locked vs. unlocked phones can be a confusing topic. So let’s see if we can explain some of the basics for you.

What is this phone lock?

The lock is really a software code that’s put on the phone by the manufacturer as per the requirement of the carrier that sells the device. And the lock is meant to ensure that the phone can’t be used on any other operator’s network until a different software code is entered to unlock the device.

This is an issue that’s most important for devices that operate on GSM networks. This is a wireless standard that used by AT&T and T-Mobile in the U.S. and by most operators around the world, especially in Europe, Asia, Canada, and Africa, as well as parts of Latin America. The 3G technologies HSPA and HSPA+ are based on GSM, which means carriers offering HSPA or HSPA+ also operate via GSM.

GSM and LTE technology need a SIM cardAll GSM devices are designed so that service is provisioned using a SIM card. With an unlocked device, a GSM smartphone can be reprovisioned and used on another network simply by popping out the old SIM card and putting in a new one from the new carrier. The carrier doesn’t necessarily need to be notified, and you don’t need anyone in the store to reprovision your phone.

GSM only? What about CDMA?

This is not the case with phones developed for CDMA networks. This is the technology used by Verizon Wireless and Sprint in the U.S. and its subsidiary prepaid services, such as Page Plus, Virgin Mobile or Boost Mobile. It’s also used by some carriers in Latin America, Asia, and Canada. The standard is not as widely used as GSM. CDMA devices do not have SIM cards. So if you wanted to take your CDMA device to another CDMA carrier, because a CDMA-only device can’t be used on a GSM network and vice versa, you’d have to get the carrier to provision the device for that other network. EV-DO is the 3G technology used on CDMA networks.

In general, CDMA carriers don’t reprovision devices made for other networks for use on their own networks. So this means phones made for Verizon, which are using the same basic technology as devices made for Sprint, won’t work on Sprint’s network. In other words, you can’t reuse a Verizon device on Sprint and vice versa.

But unlocked GSM phones from AT&T and T-Mobile will work on each other’s networks, which makes the use of GSM much more flexible than CDMA.


In summary, phone locks are not really relevant when you’re talking about 2G and 3G devices that operate on CDMA or EV-DO networks. But phone locks are very important for devices that operate on a GSM or HSPA/HSPA+ network. Almost every GSM device comes “prelocked” to a particular carrier. Certain phones are sold unlocked. And if you have a device that is locked, you can get it unlocked from your wireless carrier if you meet certain criteria, which includes paying the full price of your device or ending your contract and being in good standing with your service provider.

Is it a locked or unlocked phone?

Complicating factors

So that’s the basic gist of how software locks for smartphones work. But things are getting a bit more complicated because now there’s a new network technology that’s currently used only for data services but will eventually be used for voice too. That technology is called LTE. And like GSM, LTE uses a SIM card.

But unlike GSM, not all LTE services operate over the same radio frequency. For instance, to deliver their LTE services, AT&T and Verizon Wireless use different slivers of spectrum that have different “band plans.” This means devices built for AT&T won’t operate on Verizon’s LTE network and vice versa.

This issue will soon change as chip manufacturers start including multiple radios on their semiconductors. What’s more, wireless operators will also soon be incorporating other slivers of spectrum into their LTE networks, which will overlap with their competitors. When these things all start to converge, we’ll likely see more interoperability among devices that include support for the faster-speed LTE services.

Meanwhile, many of the smartphones being built today for Verizon and Sprint also include GSM capability on top of CDMA and LTE. If a device also supports GSM, then it has a SIM card, which can be swapped out to access almost any GSM network.

Remember that in the U.S., Verizon and Sprint customers use either a Verizon or Sprint CDMA network. The GSM radio is included in these phones so that subscribers can roam onto networks in Europe and other parts of the world. Verizon and Sprint subscribers can choose either to sign up for international roaming plans with their U.S. carrier when they travel, or, if they can get their devices unlocked, they can swap out the SIM, put in a SIM card from a local provider, and get new service that way.

Verizon 4G LTE phones are unlocked out of the box, but there is a catchIn unlocked phone SIM card can be swapped out to access almost any GSM network

One thing to note here in terms of software phone locks is that all Verizon 4G LTE smartphones come unlocked out of the box. The reason why is that the spectrum Verizon is using to build its 4G LTE network had restrictions put on it by the Federal Communications Commission aka FCC, which required the company to allow “open access” to the network. So as part of this provision, Verizon has decided not to lock those devices. That said, its 3G devices are locked.

So what does this mean for the average consumer? Let’s take the Samsung Galaxy S6 as an example. It’s a 4G LTE smartphone. A Verizon version of this phone comes unlocked out of the box. There aren’t special codes that need to be entered in order to use it on another carrier’s network. But because of the spectrum differences I mentioned above, a Verizon Galaxy S6 won’t operate on AT&T or T-Mobile’s LTE network. It will operate on AT&T / T-Mobile’s 3G network, which is based on GSM. So this means you can use the Verizon version of the Galaxy S6 on AT&T for talk and text services, but unfortunately you won’t get the fastest Internet speeds on it.

The same is true if you take the Verizon Galaxy S6 to Europe. You can swap out the SIM card and put in another carrier’s SIM card, but the device will operate only on a GSM-based 3G network. And it won’t operate on a faster 4G LTE network.

Even though the phone is unlocked and uses the same CDMA technology and some of the same radio frequency channels as Sprint, an unlocked Verizon phone won’t be able to work on Sprint’s network.

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101 Responses to “What are unlocked phones?”

  1. Will french network SFR work in english unlocked phone ?

  2. which smart phone do you prefer for straight talk? samsung or sony?

  3. Jason, can I use an unlocked galaxy s5 or note 4 with Att or t-mobile?

  4. I have a contract with AT&T and I’m wanting to buy a Samsung Galaxy S5. Will an unlocked phone work with AT&T as it uses the micro SIM card….the smaller ones but not like the iPhone SIM. I don’t want to pay full price at AT&T if I can use an unlocked phone.

    • Michelle, yes it will work. Unlocked phones are compatible with AT&T SIM cards, micro SIM cards and nano SIM cards. Let us know if you have any further questions.

  5. Melvin cruz on April 6, 2015 @ 4:34 pm

    I`m planning to buy an unlocked phone. I am from Puerto Rico my carrier is Clark will these phone will work with my current carrier?

  6. hello yes my question is is rooting the same as unlocked phone? I have a samsung galaxy s2 and I can’t get remove the sprint apps and sprint ID keeps crashing need to restart my phone. “Sprint has stopped” comes on my screen
    Each time,how can I root or unlock it??

    • Allen, rooting and unlocking phone are two different things. It looks like you need to root your phone to solve the issue. Also Sprint phones cannot be unlocked since these are CDMA phones, not GSM.

  7. pansey mcclide on October 3, 2014 @ 11:40 pm

    I have a Nokia c7-00 without a sim card that was T-moble what other carrier and sim card can I used?

  8. If I get a unlocked Samsung galaxy s3 for Verizon will that work for Straight talk?

  9. Hi I’m wanting to buy a lg g3 international phone that is unlocked, I was wondering if it will be able to work with my straight talk service?

  10. If I purchase an unlocked LG G3 will it work on Metro PCS in central Texas? I currently have a sprint iPhone 5s but I’m wanting to switch carriers obviously to save a bit of money. I check Metro’s website but there aren’t many answers there

    • Yes, the unlocked LG G3 will work. Since Metro PCS and T-Mobile merged, unlocked phones are compatible with Metro PCS SIM cards. Let us know if you have any further questions.

      • Peter Michael on October 23, 2014 @ 12:20 am

        Which version of the lg g3. International or f400, will it be able to use 4g lte data

        • Peter, all versions of the LG G3 offer 4G LTE:

          – D851 supports LTE 700 / 1700 / 1900 / 2100 / 2600
          – D855 supports LTE 700 / 800 / 900 / 1800 / 2100 / 2300 / 2600
          – D850 supports LTE 700 / 850 / 1700 / 1800 / 1900 / 2100 / 2600

          • Peter Michael on October 23, 2014 @ 12:44 pm

            So all the versions listed that can connect to 4g lte can work in metro pcs

          • Peter, I would recommend to check with Metro PCS which bands the carrier runs the 4G LTE service on in your local area. Then compare the frequencies to the model capabilities to be assured that you will have access to LTE service.

          • Peter Michael on October 23, 2014 @ 6:42 pm

            Thanks Jason, I really appreciate your feedback.

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