Mike bought a Huawei G8 mobile phone in Hong Kong that is a dual SIM model, but it only runs on the G2 band in the US, even though it's on G4 in Hong Kong. Leo says that it wasn't designed for the US market and as such, it only supports certain bands here. He may not have much of a choice. One thing he can try is going over to the XDA Developer Forums. He may be able to root the device and gain access to those bands. He should enter the exact model of the phone to find out how to do it.
How can he find out what phones work in the states from overseas? Leo says he really can't, but he should check out GSMArena. He can check his carrier for the band they support. He should find a carrier that could support the phone and switch. Or get a phone that supports the bands his carrier uses. Doctor Mom in the chatroom also shared this link from Wikipedia.