I had tmobile for quite awihle. Recently me and my wife moved to verizon (Which i think was not wise but she whinned) and i got another iphone 6 but it was verizon specific. I was not done paying on my Tmobile iPhone 6. What should do i do with the old one? Can i give it back? (it has a cracked screen) Or can i sell it on like craigslist for what i owe on it and just pay it off?