I know that unlocked AT&T phones should work on T-Mobile but the wifi calling will not work. because of this I am looking to buy a used T-Mobile Branded phone on ebay, craigslist, swappa etc. My question is will an unlocked T-Mobile phone still support wifi calling on a T-Mobile plan or will the fact that it's unlocked break that functionality? If it matters i'm getting the $30 plan from Walmart with 5GB data and 100 talk minutes. Thanks.