@SSpreitzer
The A3 should actually be able to use a large portion of the US frequencies used on AT&T (2G, 3G and min 1 LTE 4G band) and T-Mobile (2G, 3G & min 1 LTE band) , Verizon (min 1 LTE band) and thus be usable for the US....
For the other numerous providers, no idea.
The respective network coverage is not always given, especially in more remote areas.
But basically it works.