I don’t see how the history of GSM is very pertinent to the present scenario. At least in the last several years I’ve used phones from Europe or Asia or other networks in North America and they all just work with first-party or MVNO SIM cards in The US, from T-Mobile, AT&T, Tracfone, Mint, and others, assuming the device supports the appropriate bands (which varies a bit by region, especially for LTE).