[Samsung Galaxy S8+ Questions & Answers] Judson1975:
AT&T

First, AT&T. The company has rolled out a massive 4G LTE network in the United States with support for bands 2, 4, 5 and 17, but the backbone of it remains band 17 in the 700MHz range, the company's primary band. The remaining bands 2, 4 and 5 are mostly used in areas where AT&T does not have band 17, 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 phone supports all and not just one of these bands, in order for you to make maximum use of 4G LTE speeds.

Starting in the summer of 2015, AT&T has begun rolling out WCS spectrum in the 2.3GHz frequency range. Those new bands are still only available in limited areas and are considered "capacity layer" on top of AT&T's nationwide 700 MHz coverage. It's worth knowing that only a few phone today support WCS bands: the Galaxy S6 Edge+ and Galaxy Note 5 are two devices that do, but most older phones do not.

Verizon Wireless

Verizon Wireless was the first to arrive to the 4G LTE race and it has also built its nationwide network based on 700 MHz spectrum, but the primary band for Verizon is band 13. Bands 2 and 4 are used to strengthen the signal in the densely populated urban areas. One important thing to note about Verizon Wireless is that many phones are built specifically for the carrier, including its 4G LTE bands. In other words, the common case is that you will not be able to use an AT&T device on Verizon's 4G LTE network.

Sprint

As of February 2016, Sprint is finally allowed to shut down its WiMax network and expectations are that it will flip the switch off by the end of March 2016.

Sprint's 4G LTE network runs on bands 24, 25 and 41 with band 25 in the 1900 MHz range being the carrier's primary frequency. Bands 24 and 41 are used to boost the capacity of the network and its speed.

In Sprint marketing speak, markets that support all three bands are denoted as Sprint Spark compatible.

T-Mobile

Finally, T-Mobile has been the loudest and arguably the fastest growing 4G LTE network, especially in the big cities. The carrier is also one of the main bidders in a hugely important spectrum auction for the 600 MHz range that will be held by the FCC in Q1 2016 and will help T-Mobile expand its network coverage and strength.

Currently, T-Mobile's main band is still band 4 (AWS) in the 1700 MHz range. Band 2 is used only in markets where band 4 is not available.

Band 12, on the other hand, is where most of T-Mobile's growth happens. While at the beginning of the roll-out in late 2014, few phones supported band 12, in the beginning of 2016 most popular phones do and the increased penetration of the lower-frequency band makes it preferable.

Europe and China 4G LTE bands, 4G LTE support in phones

While the 700 MHz range in various bands has been the backbone of the U.S. 4G LTE coverage, in Europe and China carriers use different spectrum and bands, so phones from the United States may not work there. In Europe, most carriers base their networks on bands 3 (1800 MHz), 7 (2600 MHz) and 20 (800 MHz).

China, on the other hand, uses a whole different 4G LTE standard - while the Western world has rolled out FDD-LTE networks, China and large parts of Asia use TDD-LTE. The differences between FDD and TDD are purely technical and the main one boils down to the fact that FDD is symmetrical (1:1 upload vs download), while TDD allows variable up / down ratio. The main bands for China are TD bands 40 and 41.

Finally, it's worth noting that these days still only a few phones can truly be considered global: the iPhone 6s and iPhone 6s Plus support practically all Western bands in one phone (the full list of supported bands include 1, 2, 3, 4, 5, 7, 8, 12, 13, 17, 18, 19, 20, 25, 26, 27, 28, 29, 30), the Nexus 5X and 6P are two other phones that support a fairly comprehensive list of bands.

Found this on https://www.phonearena.com/news/Che...on-T-Mobile-and-Sprint-use-in-the-USA_id77933 I don't see band 30 listed. I'm wanting the s8+ but I want to know if I can use the international. I'm on cricket using at&t