Forget about the Walmart zip code checker. If you are able to use AT&T or T-Mobile in your area, you will be fine.
For the white phone, check out shopcelldeals.com or their storefronts on Ebay and Amazon.
When you look up the phone on Tracfone.com, look at the url bar and check the market= part. If you see GSM4 at all, then Tracfone will send you an AT&T sim. If you see GSM5 at all, then Tracfone will send you a T-Mobile sim. You can edit this, but since they don't have the white phone, I won't go into it.