One of the reps in Walmart told me how to look at the packaging and tell which phones used which carriers. I don't remember what she said but if you ask the right rep they can tell you. Might tell you which carrier would work best with your phone and your area.

I bought cheap phones on different carriers to find which ones worked best in our new location. Some phones are only $5, cheap test. I talked to the reps at the company stores to decide which ones were worth testing. They have very detailed coverage maps.