Timotheus Höttges & John Legere bet their merger on bamboozling DC on "What is 5G?" They are using New Definition 5G, introduced in 2017 and 70% to 90% slower than the good stuff, millimeter wave.
Legare is swearing to Washington the T-Mobile 640 MHz 5G NR network will be many times faster than LTE. That isn't true, of course. It's far more likely to be only 25%-50% faster, or perhaps less. It may even be slower than the 500 MHz LTE/LAA T-Mobile already has in Manhattan.
In 2016, 5G meant millimeter wave and (for some) Massive MIMO*. Millimeter wave bands had far more spectrum available, 400 or 800 MHz channels compared to 100 MHz maximum in LTE. 20 gig peaks work in the laboratory and Verizon is delivering a true gig to customers in 2018.
Folks building LTE-speed networks wanted to be called "5G" and take advantage of the massive hype. So they made "New Definition 5G" with a pr campaign and a minor software tweak, NR (New Radio.) 4G LTE networks became "5G." Every engineer in the business knows this is a scam.
T-Mobile in the U.S., China Telecom, and many others are deploying 4G speed networks and calling them 5G. They are 70% to 90% slower than the originals.