It's not just network support. Most US carriers whitelist which phones they allow on their network for "security" and "compatibility" reasons (which happen to align with the phones they make money on). So you may have a phone that has no technical reason to not work but won't because the carrier doesn't allow it. It's not all carriers so FCC certification is still valuable. It is probably less a technical reason and more a liability/legal reason as other markets have similar regulations on EMI.
You don't really have to jump through too many hoops, it is pretty easy to buy one and plug in a SIM. You just have to select the right carrier. I'm using a xiaomi 14 ultra global, selected "English" and everything works fine. Haven't run into anything in Chinese. Xiaomi's not in the US but they are in Europe so it's not that bad. Yes I have to pay upfront and didn't get trade on deals but I'm not locked to a contact and only pay $15/mo on T-Mobile. But warranty support is much harder
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