Buying Replacement Phone, What phones Are Compatable With T-Mobile Family Talk?

Had to warranty my phone. I'm looking to purchase a new one but don't like the choices at WalMart. My phone is a Nokia Lumia 520 T-Mobile Family Talk (not prepaid) Windows. What do I have to know to purchase a phone that I can just transfer my existing sim card to? There is a 521 at WalMart like mine but it's prepaid. Will the prepaid work in my case where I'm billed monthly with no contract? I'm thinking it won't. So if I'm looking to go with a different phone brand and operating system but stay with Family Talk T-Mobile what are my options? Forgive me for not being up to speed on these things...



Kind Regards, Steve