Off-Topic Question From a Techno-Idiot

If a phone is GSM UNLOCKED that means it’ll work on any network, correct? That’s what I assume, but I don’t want to buy the phone until I’m 100% certain.



  1. That means that it will work on a carrier that uses GSM like AT&T or Verizon. The other kind is CDMA. I don’t recall who uses that.

  2. You can check this by replacing the sim card with one from another network and it should work fine. I thought most carriers in N America had to do unlocked phones or unlock them upon request?

  3. It’s complicated.

    There are also different frequencies/bands as well when looking at 3G and 4G. I don’t know about 5G stuff. So some phones, even if unlocked, might not support particular bands. This can be a problem if you buy a phone intended for one market (Europe, South America) and try to use it in USA or Canada. My phone, for example, does not support all the bands used by my mobile carrier. It supports some of them and it works fine for my needs and it’s a great phone, so I’m good with it. You need a knowledgeable friend who can check a particular model to see if it will work on your network.

  4. Recently, I decided to move from Credo (which piggybacks on Sprint/CDMA) to Consumer Cellular (which piggybacks on AT&T/GSM), because it’s a lot cheaper. The iPhone 6 hardware is supposed to handle either. After much back-and-forth, Credo said they had unlocked my phone, but it still wouldn’t work with CC. I wound up having to buy a CC-branded phone. I rather like my “new” 7s, but I hate being forced to buy it. The problem was not one of inherent capability, apparently, but corporate noncooperation.

  5. Carriers in the US have to unlock a phone on request – IF it’s fully paid for. If you still owe on the phone (you bought it on a finance plan), they won’t (at least, AT&T won’t – they wouldn’t until I paid. Since I owed about $20 at that point, I just paid it). Then comes the fun part of talking to various aspects of said carrier until they finally disgorge the unlock code _and_ how to apply it (different on different phones – Samsung differs from Motorola differs (considerably) from iPhone…)

    I unlocked a phone of mine about 4 years ago. The experience was scarring enough that shortly thereafter (though not _only_ for that reason) I abandoned both AT&T and Samsung. Since then I’ve bought unlocked phones.

  6. It’s complicated.

    If this were Europe it wouldn’t be. There, any phone works with any carrier, a consumer-friendly competitive principle baked into the original GSM design. All phones are SIM-unlocked.

    It’s not like that here in the US. Our mobile carriers glower darkly at the idea of competition. In fact, the original SIM-less US CDMA phones were hardware-locked to their carriers. If you wanted to change carriers, you junked the phone and bought a new one.

    Today, if you buy an unlocked GSM phone from an independent supplier, you have a reasonably good chance of getting one that will work with any US carrier. This is generally true for 2G/3G/4G phones; I’ll leave it to someone who knows to discuss the 5G situation.

    If you buy a GSM phone from AT&T or T-Mobile and persuade them to unlock it (AT&T is reportedly sometimes less than eager on this point), you can figure that it will almost certainly work for an MVNO that uses the same towers.

    However, if you try to take an AT&T phone to T-Mobile or vice versa, the outcome isn’t so certain You may get full service, except for special carrier features. Or you may get basic voice and text service, but no data, or slow data.

    The reason is that the carriers often deliberately delete other companies’ frequency bands from the phones they sell. I get the impression that the MVNOs are less likely to neuter their phones this way, but I’m not positive about that.

    If you have a Verizon or Sprint phone, my impression is that you can usually switch to their respective MVNOs, if you can get them to unlock the phone. I don’t think that their phones will usually work properly with any other service. I have no personal experience with those carriers, however, so I welcome corrections from anyone who’s done it.

    This slippery snake slithered up and bit me several years ago. I bought an unlocked T-Mobile branded hotspot. With a long list of supported frequency bands, it was advertised as compatible with almost any carrier almost anywhere in the world. It worked fine with a T-Mobile MVNO, but when I tried it with an AT&T MVNO, I got nothing above 2G data speeds. It turned out that T-Mobile had ordered a special custom version of that hotspot. It only supported THEIR frequency bands.

  7. My last two phones could work on both CDMA and GSM networks. My MVNO, Ting, has deals with both Sprint and T-Mobile. That means I can use either network by swapping a SIM card and notifying Ting. I haven’t had a reason to bother, since both have good coverage near me.

    My previous phone worked fine in 5 European countries, so the radio band issue is not universal.

    These are non-carrier-branded phones bought unlocked.

  8. One more thing to consider if it is a relatively new phone is whether you will be able to get OS updates for the phone once it is unlocked. I once had an unlocked AT&T phone that I was using with Ting and I could not get over the air Android updates. That leads to a bunch of side loading if you want to remain up to date (trust me, you do if you use the phone for anything other than phone calls).

  9. Consumer Cellular has been very good for my wife, though she’s a light user (typical outgoing monthly use: 0; incoming use: spam calls only).

    Boise Ed: Consumer Cellular uses AT&T and T-Mobile networks, or at least they did when she signed up a year or so ago. If anyone is switching to them, it’s worth asking neighbors to find out whether one of the two is better in your neighborhood. Mostly it won’t matter, but you’d hate to have missed the opportunity!

  10. Per PC magazine online – “In the US, Sprint, Verizon, and US Cellular use CDMA. AT&T and T-Mobile use GSM. Most of the rest of the world uses GSM. The global spread of GSM came about because in 1987, Europe mandated the technology by law, and because GSM comes from an industry consortium.”

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