There are two types of 5G networks: The ultra-fast, 2Gbps mmWave technology most prominently deployed by Verizon, and the barely-faster-than-4G sub-6GHz system that has a much better range and penetration than its faster sibling. AT&T has been offering the latter since late 2019 in a few cities, but it now has announced that it will also open its own mmWave network to the public starting Friday, calling it "5G+."
The launch of AT&T's network coincides with the release of the Galaxy S20+ and S20 Ultra, which support both mmWave and sub-6GHz thanks to their Snapdragon 865 chip. This will make them the only phones to support all of AT&T's networks for now, as the regular S20 only works on sub-6GHz 5G. That might not be too much of an issue, though, since mmWave's range is severely limited, so even if you have an S20+ or an S20 Ultra, you'll see yourself using 4G or sub-6GHz 5G most of the time anyway.
At the moment, the ultra-fast shortwave technology is only available in a few locations, beginning with "select businesses, universities, hospitals, and sports venues" — that's how short mmWave's range is. You can find more information on 5G availability over at AT&T's website.
- The Verge