Which US operators do not block the GSM module in mobile phones?

Question

Mobile devices

<Greetings.
I had the experience of buying several Android and iPhone devices, Verizon and USCellural do not block the GSM module and when buying such phones, even with the bad esn mark, you can absolutely safely use, for example, in Russia or Ukraine, the phone accepts a SIM card, registers on the network, 4G, sms, voice works .
But what other operators allow this?
Interested for iPhone above 7ki and for most modern Android devices is a certain compatibility list: where exactly you need to unlock (for example, like T-Mobile or Sprint), and where there is some kind of freebie)

iPhone operators example