My wife has US Cellular and was thinking about buying a used Iphone. Does anyone know if you just buy an unlocked Iphone for US celluar? Any good places to buy? She currently has an Iphone 6 so we would be looking for a 7 plus or newer and currently more than the 16GB of memory she has now. It seems when I do a search like on swappa.com us cellular doesn't have very many options.Thanks in advance