So, I'm on a solo contact while my mom is on a mobile-share contract. One of my mother's line's is due for an upgrade but she care about using it. My question is: Can I use my mother's upgrade and simply put my sim card in the iPhone 6 once it arrives even though I am on a different contact? I have seen plenty of times where people have used someone else's upgrade but they've all been on the same line. Has anyone done this before?