Mobile / Features

Unlocked Phones and Your Carrier: How They Work Together

In our last article, we spoke about things you needed to know about buying an unlocked phone, including the freedom of being off contract, and the wide selection of phones available. We also gave you some insight into phone variants and manufacturer warranties. Now, we’re going to discuss phone frequencies and bands, and walk you through some steps to help assure that your new unlocked phone works with your carrier.

A guide to cell network protocols and generations

Cell phone network technology is always improving and getting faster. To help customers differentiate between data speeds, many networks and phone manufacturers tend to group things together by generation. You are probably used to seeing the 2G, 3G, and 4G monikers used. What you may not know is that each generation contains many different small upgrades, and in the case of GSM and CDMA networks, completely different technologies. Below is a chart outlining the family tree.

You may be wondering why there is no 4G CDMA Based Cell Protocol, even though CDMA carriers offer 4G LTE service. LTE is a GSM standard, even though it is used by CDMA carriers like Verizon and Sprint. This is why Verizon and Sprint phones with 4G LTE have SIM card slots.

As you can see, there are different types of 2G, 3G, and even 4G. And, to make matters even more confusing, different carriers and phone manufacturers classify certain protocols as different generations.

For example, in the United States, T-Mobile and AT&T brand High-Speed Packet Access (HSPA+) as 4G. This is why Verizon and AT&T's 4G cell coverage maps look so different in commercials. The reason they do this is that HSPA+'s maximum speed of 42 Mb/s is almost as fast as category one LTE at 50 Mb/s. And the fastest CDMA 3G data protocol, EV-DO Rev. A, tops out at 3.1 Mb/s. So to their marketing teams, it probably made sense to pit 42 Mb/s HSPA+ against 50 Mb/s LTE than the 3.1 Mb/s 3G CDMA network to which customers were accustomed.

However, the rest of the world never had slow CDMA networks to which to compare speeds, and since HSPA+ is really more of an upgrade to Universal Mobile Telecommunications System (UMTS) 3G rather than a totally new protocol, they kept calling it 3G. So, unlocked phones free from AT&T and T-Mobile firmware will not say they are connected to a 4G network when connected to what AT&T and T-Mobile call 4G (as opposed to 4G LTE). You will either see a 3G, H+, or something similar. The reverse is also true if you get an AT&T or T-Mobile-branded phone. Because of the firmware, your phone will register as being on 4G even when connected to what your carrier considers to be 3G. This doesn't affect performance in any way. To make things simple, we use consistent definitions on all our phone write-ups at B&H, regardless of how the phone’s firmware defines certain protocols. Those rules are as follows:

3.5G HSPA+
2G CDMA and IS-95
3G CDMA2000 and EV-DO

As you will see later, this makes it much easier to determine what phones will work with what network.

Phone frequencies and frequency bands

So, on top of all the cell-phone protocols, there are also cell phone frequency bands. To avoid interference, different parts of the electromagnetic spectrum have been allocated for different uses. Radio stations get one part of the spectrum. Cell phones use higher frequencies than radio stations, and mostly lower frequencies than Wi-Fi, much in the same way radio stations broadcast on only one frequency (93.6 MHz, 99.7 MHz, etc). Cell-phone companies get licenses to use certain frequencies in certain areas. These differ slightly from region to region. To work with your wireless carrier, you phone must support the frequencies your wireless carrier uses. It’s for this reason that all unlocked phones won’t work perfectly with all carriers.

When it comes to 2G, there are only four commonly used GSM frequencies: 850, 900, 1800, and 1900. Fortunately, just about every GSM phone on the market supports all four of those bands. As long as your cell provider has an active 2G GSM network, you don't have to fret about that.

For UMTS 3G, there are five common frequencies used around the world: 850, 900, 1700 (AWS), 1900, and 2100. Here, you need to be a little careful if you are looking for full compatibility, especially if you are on a carrier using 1700 (AWS), as that isn't a widely used frequency band. Still, there are a number of phones that support all five 3G bands, so if you want, you can have it all.

For LTE, things get much more complicated. LTE involves pieces of spectrum that were recently allocated for cell phone use. In the United States we have repurposed much of the old UHF-TV-station spectrum for various cell carriers, through auctions. In the US, certain carriers own rights to certain frequencies that don't line up with the parts of old TV spectrum carriers in other countries use. In fact, there are more than 40 different LTE-frequency bands used around the world—so many, that you can't be sure a phone will work by just looking at the supported MHz. For example, 700 MHz could be Band 17, Band 12, Band 13, Band 28, or Band 44. Each of these uses slightly different frequency allocations, around 700 MHz. For this reason, at B&H we use Band numbers when referring to supported LTE frequencies, as they are far more specific.

For quick reference here are the frequencies used by US carriers:

This table is a screenshot from the B&H e-commerce website. You can also find a full list of worldwide GSM carriers at this link.

How to ensure your unlocked phone will work with your carrier        

Now you know enough to purchase an unlocked smartphone confidently, and all you need to do to make sure your new phone works perfectly is follow these four easy steps.

1. Choose Your Wireless GSM Carrier  If you are in the United States and want to use an unlocked phone, you have the choice of AT&T and T-Mobile primary networks, or any one of the many Mobile Virtual Network Operators that use their networks. Generally, MVNO's have lower prices but have fewer high-end phones available in-store, which is no problem if you bring your own unlocked smartphone. As noted above, Metro PCS (T-Mobile) and Cricket (AT&T) are two MVNO's that are owned and operated by their parent companies as a lower-price alternative.

If you live elsewhere, then pretty much every network uses GSM for voice. Many Canadian networks use CDMA for 2G service, but transitioned to GSM for 3G and 4G, so unless you really want 2G service, you will be fine with an unlocked phone.

2. Check what frequencies your carrier uses  Once you've decided which carrier you will be using, the next step is to check which frequencies that carrier uses. We have compiled a list of most worldwide GSM carriers and what frequencies they use, which can be found here.

So, say you are planning to use AT&T, or any AT&T MVNO as your carrier. Looking at the chart, you can see that AT&T uses 850 and 1900 MHz for 2G and 3G service and bands 2, 4, and 17 for LTE. That means any phone that supports all those frequencies will be 100% compatible with AT&T. It’s quite simple.

Remember that some US carriers call upgraded 3G (HSPA+) “4G”, and LTE “4G LTE”. At B&H, we use 3.5G to be consistent with worldwide standards. It makes it easier, because HSPA+ uses the same frequency bands as 3G UMTS, and is always backwards compatible, where LTE uses a completely different set of frequencies.

3. Choose the right phone variant for your carrier

Now that you know what frequencies your cell carrier uses, you just need to make sure to get a variant of the phone you want that supports those frequencies. The frequencies a phone supports can be found in the specifications tab under cellular network, and will look like this:

This is a sample table of specs from one of the unlocked phones that B&H sells.

By looking at this table, you can see this phone supports all AT&T and T-Mobile 2G and 3G frequencies, and all AT&T LTE frequencies, and most T-Mobile LTE frequencies. Furthermore, the LTE frequency it lacks for T-Mobile is Band 12, which is newly deployed and only available in a few markets in addition to Band 4, meaning it will get full coverage everywhere on both AT&T and T-Mobile. As long as frequencies match up, you can be sure that the phone will work fully with your carrier; you just need to insert the SIM card.

4. Setting up your phone  The last step is to make sure everything is set up properly on your new phone. The set-up process will differ from customer to customer, from carrier to carrier. Basically, you need to make sure the APN and MMS settings are set up correctly on your phone, and that your carrier has your account set for the fastest data speeds. With some carriers, these will be downloaded automatically when you first start up your phone. With other carriers, you will need to look up what their current APN and MMS settings are, on the carrier’s website or through sales representatives.

This setup process should be painless, but many US carriers do not train their staff as well as they should when it comes to setting up an unlocked phone. Also, some carriers restrict LTE service based on the International Mobile Station Equipment Identity (IMEI) number listed in your account. Remember, a GSM carrier can't actually tell what IMEI number your phone has unless you tell them, because service is linked to the SIM card. If you are with a carrier that doesn't list your unlocked phone as being LTE capable based on the IMEI number you give them, even though you know it is LTE capable, you can always just give them an IMEI number of a carrier-branded phone. Or set up your account on a carrier-branded phone first, and then switch the SIM card into the unlocked phone.

So, that’s it. Hopefully this has helped. I'm sure you are an expert now but, just in case, if you have any questions feel free to ask the sales staff at B&H, or just comment below.

Discussion 4

Add new comment

Add comment Cancel

The chart referenced twice in the article does not show the carrier frequencies for Verizon.

We don't list CDMA carriers like Verizon (or Sprint) in that chart because they won't work with unlocked GSM phones. Even if they work on the same frequencies, they speak different languages. For more info on the topic please check out my previous article about buying and unlocked phone  That said, both Verizon and Sprint use 800 and 1900 MHz for 2G and 3G, and Verizon uses bands 4 and 13 for LTE.

High tech stuffmade easy for laymen. Thanks. 

What if I bought an iPhone in the US to be used in Brazil?

Luckily, Apple likes to make as few variants as possible. Both iPhone 6S and 6S+ Variants sold in the US by Apple support a huge number of LTE bands, including all 2G, 3G, and LTE bands currently used by Brazilian carriers. The hard part will be getting your hands on an Unlocked iPhone. I believe you can find them SIM free at Apple Retail Stores.