Yeah not likely indeed. The list is not exactly in stone but with your prior experience after volte came out, that would be the conclusion.
You can verify this by making a call and staying on it, go to settings, about phone, status information, sim card status - look for mobile voice network type and see if it says UMTS. I suspect it will. But maybe it will say LTE. Only when on a call.
A little wording similarity here, our non-volte-enabled phones currently sit waiting on LTE. Then they "fallback" to 3G UMTS for a call. One could say that when roaming on T-Mobile that the phone "falls back" to 2G GSM for the call, bypassing 3G. The weird part is that this might not happen in all areas. In some areas it will but in other areas you might need to change to 2G GSM manually. Text will work there as well. Then when you need data you switch back to 4G LTE.
So when you go next time, when you are able to connect to a US tower (T-Mobile) (either by land crossing or taxiing in after landing) connect manually to T-Mobile. You might be able to make and receive calls. Or change to 2G GSM manually.
The thing to be aware of is that coverage will be less than ideal. And non-existent in Alaska.
