Can I sell my replacement iPhone 5s?

My iPhone 5s had water damage it wouldn't turn on. I called T Mobile right away and got next day shipping on a replacement phone.

Of course I paid a fee, however the next morning I tried to turn on my phone and it has been working completely fine. I now have two iPhone 5s.

My nephew needs a phone but I'm thinking about selling the phone to someone so I can get my money back.

Is this possible? Will the phone work for my nephew? I didn't open the phone yet it's still in its box completely wrapped.

Will it reject my nephews SIM card because it isn't mine? Or should it be fine?

Sure why not