We work with AT&T and T-Mobile as last mile carriers. As such we are restricted to their frequency bands. If you dont know which those might be, or even what that means, don't worry! See an explanation for them below.
AT&T has rolled out a massive 4G LTE network in the United States with support for bands 2, 4, 5 and 12.
The remaining bands 2, 4 and 5 are mostly used in areas where AT&T does not have band 12, while in the densely populated metros, AT&T combines spectrum from multiple bands for better coverage. This is the reason why it is important that your modem supports all and not just one of these bands, in order for you to make maximum use of 4G LTE speeds.
Here is a breakdown of all the individual bands at AT&T and their roles:
Band 2 (1900MHz frequency range): it is one of the core bands for AT&T LTE as the carrier has large, 20x20MHz blocks in most markets.
Band 4 (AWS-1700/2100MHz): this band is used as a supplement for improved capacity and is usually deployed in small, 5x5MHz blocks.
Band 5 (850MHz): this band is used most commonly 3G (HSPA+ ) connectivity, but some of it also goes toward LTE. AT&T owns a lot in this frequency range throughout the nation, and band 5 is sometimes used in areas where there is no band 12 coverage.
Band 12/17 (700MHz): the backbone of AT&T's LTE network and it provides practically a nation-wide coverage.
Band 30 (WCS 2300MHz): another supplementary band for 4G LTE. AT&T has deployed chunks of 10x10 across the nation.
Band 66 (AWS-3-1700/2100MHz): band 66 is a superset of band 4, meaning that it includes all of the band 4 blocks plus adds a few more. AT&T usually deploys this in 10x10 chunks, and you could commonly see it in the New York and New Jersey areas. It is actively being deployed across the country.
T-Mobile has been the loudest and arguably the fastest growing 4G LTE network, especially in the big cities.
Currently, T-Mobile's main band is still band 4 (AWS) in the 1700 MHz range. It is the band T-Mobile uses in densely populated areas and while it may not quite have the penetration capabilities that come with B2, it is considered more stable. Historically, T-Mobile used band 4 back in the times of HSPA+ networks and has later on repurposed the frequency for 4G LTE, plus it has added additional coverage to the band via the MetroPCS acquisition. Band 2, on the other hand, is used in markets where band 4 is not available, but the two are also aggregated for better coverage in markets, where both are available. You can typically see band 2 used in rural/suburban areas.
T-Mobile has also won a big, 30MHz chunk of spectrum in an auction held in summer of 2017. The frequencies that it is now allowed to operate are in the low-band, 600MHz band, and are referred to as 4G LTE band 71. Interestingly, band 71 uses old UHF TV frequencies, and it will be relying more on them in the future as TV stations clear them. At the end of 2018, there were over 800 cities and towns that support the new longer range band 71. These frequencies are also expected to become the base for T-Mobile's upcoming 5G network, while at the current time, they contribute the most to the company's small city and rural coverage. The full deployment of band 71 is expected to boost T-Mobile coverage by 6 million additional people.
Band 12 is similar to the newer band 71 in that T-Mobile describes both as "extended range LTE". The one key advantage of band 12 over band 71 is that it is available on many more phones. Band 71 is currently available on later models like the 2018 family of iPhones and it is the band that T-Mobile will be using to expand the network in the future.
And here is an overview of all the bands:
Band 2 (1900MHz frequency range): this is a band mostly used in rural areas, or where band 4 is not available. It has higher reach, and it is widely used in the Northeast to provide 4G coverage to distant places. T-Mobile has deployed various chunks of spectrum, from smaller 5x5 blocks to larger and speedier 20x20 blocks. This band is also used for 2G and 3G.
Band 4 (1700MHz/2100MHz): the backbone of T-Mobile's LTE network. It is usually deployed in large 20x20MHz chunks in most markets, providing fast speed and a stable connection. Used for more densely populated areas.
Band 5 (850MHz): Extremely limited use. Most band 5 coverage is offered by Verizon and AT&T. T-Mobile only operates LTE on this band around the Myrtle Beach, South Carolina area.
Band 12 (700MHz): an "extended range LTE" band, used mostly as a complimentary band for coverage in rural and suburban areas, and it is similar to band 71 in function. It is supported on most phones.
Band 66 (1700/2100MHz): an extension (superset) of band 4, this band is supported on devices since late 2016. Available in small 5x5MHz chunks and is not yet widely deployed because Federal Agencies need to clear the bands first.
Band 71 (600MHz): the big win of the FCC auction for T-Mobile, this band was previously used by UHF TV stations. T-Mobile owns band 71 all across the nation in big chunks, and will be deploying it in the near future. Since this is a 600MHz range band, it will have wider coverage and will improve coverage inside buildings. It is supported only by newer phones like the 2018 series of iPhones.