Will a Verizon Moto X really work on AT&T and T-Mobile?

The dream of taking any mobile device to any wireless carrier may soon become a reality.

The wireless market is going through a massive technological shift right now, one that will eventually make it possible to take your smartphone from one network and use it another. The switch to 4G LTE technology and the use of more spectrum bands to deploy this service will help make devices interoperable in a way they never could be using older 2G and 3G technologies.

Although change is coming, network operators haven't fully made this transition. As a result, handset manufacturers still make multiple versions of the same device supporting different radio technologies. Thanks to advances in chip technology that pack more radios into each device, some smartphones still manage to cross big technological divides. But figuring out which version of which device is compatible with which network can be very tricky.

In this edition of Ask Maggie, I help a couple of readers navigate this confusing maze of technical specifications.

Can I use my unlocked Moto X on any wireless carrier?

Dear Maggie,

Since cell phone plans and prices are complicated, as you've mentioned in a previous article, and tend to change so often, I'm drawn to the appeal of off-contract cell phone plans. I'm also a fan of the Moto X, something else you've mentioned in at least one previous article. I'm still a bit fuzzy on the details of unlocked phones and CDMA vs. GSM technology, but I am wondering if there is any way to buy a Moto X that is capable of being used on both GSM (AT&T and T-Mobile service) and CDMA (Verizon, US Cellular, and Sprint) networks.

My goal is to be able to switch among various carriers' off-contract plans as their pricing and features change. While I realize they may not change very often, I hope to be able to use a new phone, such as the Moto X for a while and I hate the idea of having to buy a new phone if I switch carriers.

I've skimmed through various discussion boards on the Internet that say the Moto X comes with both CDMA and GSM radios, and that Verizon 4G LTE phones are "world phones" that are GSM capable, but the verdict on the phone's interoperability still eludes me. Would you be able to shed some light on whether there is any hope for me?

Thanks

Cell Carrier Commitment Issues

Dear Cell Carrier Commitment Issues,

This is a great question. With phones like the Moto X available for prices as low as $350 and $400 without a contract, it really makes buying your own device and foregoing a contract worthwhile. But figuring out which phones work on which networks is tricky.

The official advice on this from Motorola is that you should buy the phone that is designed for a specific carrier's network.

"While devices may have common technologies and spectrum bands, each device is optimized for the specific carrier configuration so even when unlocked, certain network features may not be available," a spokeswoman told me via email.

The Motorola spokeswoman has a point, but the truth is that it is getting easier to take your smartphone to another carrier. That said, in order to get the most flexibility out of a single device, you have to be careful about which version you buy. For example, an "unlocked" phone, which generally operates solely on a GSM network, is usually bought at full price from the device manufacturer.

Any other phone sold through a particular wireless operator or activated through a carrier when you purchase it is usually locked to that specific carrier. This simply means it has a software lock on it that very often can be removed by calling the operator to get the unlock code. You may have to fulfill certain requirements from the carrier in order to get this unlock code. Keep in mind that carrier locks can still be on phones that are bought full price through a carrier. In other words, just because you paid full retail for the phone and are not on a contract that doesn't mean your phone is automatically unlocked. For instance, all the phones sold through T-Mobile are locked to T-Mobile. If you want to use it on AT&T, you'll have to get it unlocked.

Verizon Wireless is the only major wireless carrier today that does not put a software lock on any of its 4G LTE smartphones. This means that whether you are on a contract or you paid full price for your Verizon 4G LTE handset, it is automatically unlocked. (Note: This is only for 4G LTE phones, and it is not the case for 3G devices on Verizon.)

Aside from having a locked or unlocked phone, the other thing you need to keep in mind if you plan to take your smartphone from one carrier to another is that there are often multiple versions of the same phone sold by different carriers. And some of these will work fine on certain carriers and others won't.

Figuring out which hardware works on which network is tricky, even for experts such as myself and CNET Reviews Senior Editor Brian Bennett. In order to help answer your question, we spent a good portion of an afternoon researching and testing smartphones and SIM cards from different carriers to see what type of service we'd actually be able to get on different versions of the Moto X.

What we discovered is that a Moto X designed for Verizon will work with either an AT&T or T-Mobile service. But you may be limited in terms of the service that you can access. As you are aware, Verizon is a CDMA operator, which generally means that the radios in its devices are not compatible with the technology used by AT&T or T-Mobile. But because the Moto X is a so-called "world phone," which means it can be used overseas, it also supports GSM and UMTS technology, which are the network technologies used throughout most of the world and by AT&T and T-Mobile here in the US.

Verizon and Sprint sell so-called "world phones" so that their customers can roam when they're traveling internationally. A by product of this functionality is the fact that it also makes their devices technically compatible with AT&T and T-Mobile GSM networks here in the States.

Because the Verizon Moto X supports GSM as well as CDMA, you can get basic voice, text messaging, and 3G data service when you put an AT&T or T-Mobile SIM card in it. And you may be able to get 4G LTE service from AT&T or T-Mobile, but you may not.

Why? Even though AT&T, Sprint, T-Mobile and Verizon are all using the same 4G LTE network technology for their next-generation wireless service, they are not using the same radio frequency to deploy the service. And if the device you are using doesn't support the network technology operating on the same frequencies as another carrier, then it won't work.

This has made device interoperability tricky for handset makers and consumers. For example, Verizon, which was the first major carrier to deploy LTE in the US, initially built its network using a sliver of 700MHz wireless spectrum that only it owned. As a result, its early LTE devices only supported LTE service for what is known as Band 13. Because no one else has deployed LTE in this sliver of spectrum, no other carriers support Band 13 in their devices.

But because demand for wireless data is increasing, wireless operators are starting to deploy LTE using other slivers of spectrum. In Verizon's case, it is now deploying spectrum in what's known as the AWS band (1700MHz -2100MHz). This means that Verizon devices that now support 4G LTE must also include a new radio frequency band, which is called Band 4.

The good thing about AWS spectrum, which uses the Band 4 device specifications, is that several other carriers are also using this sliver of spectrum for their 4G LTE networks. AT&T and T-Mobile also use AWS spectrum for LTE and therefore their devices support Band 4 LTE radios.

What this means for consumers is that devices that support Band 4 radios for LTE will, in theory, be able to operate on any network that is deploying the AWS spectrum. The Verizon version of the Moto X does support Band 4. So it should be able to get LTE from either AT&T or T-Mobile. But whether or not you actually get that service depends on whether the carrier has deployed LTE in that frequency band in the geographic location where you are using your device. It could also depend on the quality of the radio or where you are standing or any number of other factors.

Unfortunately, when Brian and I tested the Moto X, we did not see any LTE signal from either AT&T or T-Mobile. Exactly, why we didn't see the service, I can't explain. AT&T and T-Mobile each use AWS spectrum for 4G LTE service in New York City. And when we popped in these same SIM cards into other devices, we were able to get LTE service from AT&T and T-Mobile.

In addition to the Moto X, there are plenty of other Verizon 4G LTE smartphones that also support Band 4. For example, the iPhone 5S, the new HTC One, and even the Motorola Droid Maxx all support Band 4 along with the traditional Band 13 for LTE. When Brian and I tested the new HTC One and Droid Maxx to see if they'd get 4G LTE access on AT&T and T-Mobile in New York City, we found that they did.

What does this mean for consumers buying smartphones off contract?
If you'd like the flexibility to switch wireless carriers without getting a new phone, it means that you need to educate yourself on the different technologies and frequency bands supported on the various carriers. And second it means, you need to carefully check the spec sheet of the device you plan to buy. Then you can match the technologies and frequencies supported on the device with the appropriate service.

In general, phones designed for GSM networks interoperate easily with each other. And if a CDMA device also has GSM support, it also tends to work well on a GSM network.

But unlocked GSM devices or smartphones made for AT&T and T-Mobile will not get basic voice or texting service on any CDMA network, such as Verizon or Sprint. The reason is that these phones do not support CDMA technology. So at this point, it's not useful to try to take a GSM phone to either of these carriers or any other operators using CDMA for voice and 3G data service.

Things get trickier when you're buying a phone designed for the CDMA carriers, such as Verizon and Sprint. Even though Verizon and Sprint use the same basic CDMA voice and 3G technology on similar spectrum frequencies,, devices are not interoperable. CDMA devices do not use SIM cards, which means service must be provisioned by the carrier. And Verizon and Sprint do not allow each other's devices to be used on their networks. I'm sure there are ways to hack devices to this, but it's not an easy process. For the most part, if you switch from Verizon to Sprint or vice versa, it requires that you buy a new handset.

That said, because most if not all new Verizon and Sprint smartphones are "world phones," they also include GSM functionality. This means they have a SIM card. So if you can get the device unlocked or if in the case of Verizon it comes to you unlocked, you should be able to put a SIM card in it from any GSM carrier and it will offer basic voice, texting and 3G data. Whether it will also support LTE depends on what LTE frequency bands are supported in the phone.

Unfortunately for Sprint customers, the carrier is using spectrum for its LTE network that no one else is currently using. This includes 800MHz, 1900MHz, and 2500MHz spectrum. Since it doesn't use any AWS spectrum for 4G LTE, its devices don't need Band 4 radios, which is currently the only unifying LTE band in the US used by AT&T, T-Mobile and Verizon.

Now, there's a chance that Band 4 may be included in certain phones sold on Sprint's network. That's likely because the manufacturer has made a single "CDMA" version of the device, which it sells to Verizon and Sprint. But just because it might support that technology, it doesn't mean that the function is turned on in the phone. So there's a chance that the device may support the appropriate technology, but because it was a device made for Sprint it doesn't actually use the functionality.

Sprint recently announced that starting next year it will begin including Band 12 in some of its devices. This is a band class used for lower 700MHz spectrum. Sprint doesn't own licenses in this band nor does it plan to deploy its own network in this spectrum. But the company has launched two partnership programs to work with smaller rural operators, which own this 700MHz spectrum and plan to build out their 4G LTE networks using it. Most rural operators as well as T-Mobile through a recent transaction with Verizon own this lower 700MHz spectrum. LTE networks haven't yet been built using this spectrum, but that should be happening in the next year.

What this means is that Band 12 could also become another 4G LTE interoperability band, especially after AT&T begins including it in its LTE devices. Last year under pressure from the Federal Communications Commission, AT&T agreed to use Band 12 instead of its current Band 17 for lower 700MHz spectrum. Once it starts rolling out devices with Band 12, smartphones from AT&T, Sprint and T-Mobile will all be compatible for 4GLTE service.

The Bottom Line:
Unfortunately, there aren't any devices today that work perfectly on every carrier. But a basic rule of thumb is that unlocked GSM phones, such as the Google Nexus devices, and phones designed for AT&T and T-Mobile will work reasonably well on most GSM networks. In the US, that means they'll work pretty well on AT&T and T-Mobile. But you should probably still check the device spec sheets just to make sure.

And remember that these GSM-based smartphones won't work at all on a CDMA carrier's network. Also, if you buy the phone through AT&T or T-Mobile or comes with AT&T or T-Mobile service, it is likely locked, even if you paid full retail price for it. You can get it unlocked, but you'll have to request an unlock code and meet the requirements of your carrier.

If you want a bit more flexibility, you could buy a 4G LTE smartphone from Verizon. You can buy the device at full price without a contract, and if it's a 4G LTE smartphone (not a 3G device) it will come without a software out-of-the box. If you go this route, you should still check the specifications of the device carefully to ensure that the Verizon smartphone you're purchasing supports Band 4 for LTE. This will indicate that it is compatible with AT&T and T-Mobile LTE networks.

I hope this answer was helpful. And good luck.

Why can't my 4G LTE smartphone work on any LTE network?

Dear Maggie,

If all the major wireless carriers are using LTE for their next generation networks, then why aren't all the devices interoperable? I know that there is a big difference between CDMA and GSM. I understand that my AT&T phone won't work on Verizon. But I thought that LTE was supposed to end this.

I'm just frustrated that I can't buy one LTE phone and have it work on any operator I want. Will I ever be able to do this?

Thanks,

Confused about LTE

Dear Confused about LTE,

I understand your frustration. As you noted in your question CDMA and GSM technologies are incompatible network technologies. As a result, devices built for one of these technologies can't work on a network supporting the other. Some device makers have added additional support in phones, so that CDMA "world phones" from carriers like Verizon and Sprint can operate on GSM networks.

But you are correct that for the most part this divide between CDMA and GSM has split the US cellular market into two when it comes to device compatibility. AT&T and T-Mobile are on one side with GSM devices and Verizon and Sprint are on the other with CDMA.

You are also correct that all the major US operators in the US and around the world have finally settled on a common network technology called LTE to build their next generation of network. This is terrific news for consumers, because eventually it should lead to more device interoperability and hopefully true global network roaming.

But before you get too excited, we aren't quite there yet. There are still two main obstacles standing in the way of full device interoperability. The first is the fact that wireless operators have deployed their 4G LTE networks in different spectrum bands. As I explained to the previous reader, when Verizon first deployed its LTE network it used a sliver of spectrum that only it owns. So there was no need for it or any other carrier to include the Verizon radio band for LTE in their devices.

The second obstacle to device interoperability is that wireless operators haven't yet started putting voice traffic on their LTE networks. Instead they still use their older 2G and 3G networks which are either GSM or CDMA based for voice and text messaging traffic. This means that even if the LTE spectrum bands were fully compatible subscribers would still be limited by the old CDMA/GSM restrictions.

The good news is that things are starting to change on each of these fronts. In terms of spectrum bands, wireless operators are beginning to use more slivers of spectrum to add capacity to their wireless networks. For instance, as I explained above, Verizon has added AWS spectrum to its LTE network, which means it has to support another band of radio frequency in its devices.

This AWS band of spectrum Verizon is using is also supported by T-Mobile and AT&T, which means their devices also use the AWS spectrum for LTE service. And this means the devices for all three carriers are compatible when it comes to LTE.

Something else that should help "harmonize" the spectrum bands used for LTE service among carriers are two wireless spectrum auctions that the FCC has in the works. The first is an auction to sell another sliver of AWS spectrum. That is scheduled for September. The good news so far when it comes to this auction is that the FCC rules, which were announced just this week, require that devices using this spectrum be interoperable.

The next big auction on the FCC's docket is the so-called incentive TV broadcast auction, which will auction off excess TV spectrum in the 600MHz frequency band. It's scheduled for the middle of next year. And again every major wireless operator as well as many small rural and regional operators are expected to participate in this auction. Rules for the auction haven't been finalized, but there is a good chance the FCC will also require devices used with this spectrum to be interoperable.

If all four major US operators are able to acquire spectrum in these two upcoming auctions, it could mean one or two more spectrum bands that will be commonly used for 4G LTE service by the major carriers. And that will result in more devices supporting the same network technology at the same spectrum frequencies, thus leading to more interoperability among devices.

Another important development on the device interoperability front is that Sprint said last week that it plans to include a band in some of its future 4G LTE devices in a frequency it doesn't even currently use for 4G LTE. Why? The carrier is hoping to partner with smaller operators that do use this frequency band in effort to virtually expand its network footprint. It also happens to be a spectrum band that T-Mobile will soon support, and that AT&T is also slated to support in the next couple of years.

Again, what this means for consumers who want to take their device to other networks is that once major operators are using common spectrum bands for LTE there are no major technical barriers that prevent devices from working on different networks.

The final piece to the interoperability puzzle will be the emergence of Voice over LTE technology, which will replace the older CDMA and GSM-based voice networks that wireless operators currently operate today. Once this happens, there will no longer be any technical reason why an AT&T or T-Mobile smartphone won't work on either Verizon's or Sprint's LTE networks. Voice over LTE deployment should begin sometime this year. Of course, it will take a long time before the older voice networks are phased out. But once VoLTE is widely deployed it will level the playing field in terms of interoperability among all US carriers.

Of course, wireless operators may try to thwart device portability. Even though the technology hurdles might be eliminated, the operators could still cripple phones with software locks that restrict their use on competing networks. Still, I am optimistic that the unlocked device market will continue to grow, especially if carriers such as AT&T and T-Mobile continue to sell services that offer customers monthly service price cuts if they use phones they've already paid for. And once the technical barriers are no longer an issue, I think more device makers will address this market. Hopefully, we will soon see smartphones hitting the US market priced below the $200 and $300 mark.

The bottom line:
Even though device portability is a little easier today than it was in the past, it's still not where it should be or where it needs to be in order to allow consumers to buy any device they want and put it on any US carrier network. But the good news is that the technology is changing the old rules. And that is ultimately a good thing for consumers.

Correction 2:00 pm PT: This story was corrected to reflect that the Moto X from Verizon does include support for Band 4. A previous version of this story incorrectly stated the LTE bands that it supports.

Ask Maggie is an advice column that answers readers' wireless and broadband questions. If you have a question, I'd love to hear from you. Please send me an e-mail at maggie dot reardon at cbs dot com. And please put "Ask Maggie" in the subject header. You can also follow me on Facebook on my Ask Maggie page.