[Q] Recommend an Android phone for me! topic

I have done some searching and I am having a hard time finding the info I am looking for. I have a T-mobile plan and I need the wifi calling. I am looking for a newer phone (galaxy S5/LG G3) and I am having a hard time finding which phones can have a stock T-mobile rom put on them to enable wifi calling. I will be buying off Craigslist so I would rather not get a t-mobile version in case the ESN gets locked. Sprint always seems to be the cheapest phones. Any recommendations are appreciated. Max price is probably about 0. Thanks!