how to tell if a phone works on a carrier

[corvairbob]

i'm looking on ebay for a phone to use on metropcs as that is my service. i found one that sasi t-mobile and metropcs. i know metro and t-mobile are the same. but when i went to willmyphonework site it show this t-mobile phone with less coverage than metropcs. and the model is a t-mobile phone. so i wonder it that site is a good site or if there may be a better site to use to find out what carriers work on what phones.

or if someone here has the Samsung Galaxy Avant G386T and is using it on the metropcs service. i would like to to find out before i was to buy one and then find out it is not compatible with metropcs. thanks.