I have a friend from Australia visiting who is using a Galaxy S4, which is unlocked.
Here are the specs:
http://www.samsung.com/au/consumer/mobile-phone/smartphone/smartphone/GT-I9505ZKAXSA
I'm looking into getting a prepaid SIM card from Verizon or At&T, but I am not sure if one will support the phone better than the other. Does anyone have an idea?