T-Mobile USA has come a long way since its spectrum-starved days, when it was forced to run 3G in an AWS band, out of sync with the rest of the world. It made increasingly efficient use of its holdings, and made a huge bet on 600 MHz when that was auctioned in 2017, enabling it to roll out broad 5G coverage well ahead of rivals. But the real turning point came with the acquisition of Sprint and its plentiful 2.5 GHz assets, enabling TMO to assemble its 5G “spectrum layer cake”, with 600 MHz for coverage, 2.5 GHz for capacity and millimeter wave for fixed wireless and hotspots. It has not stopped adding to its arsenal however. This month…