What would happen if i sold a iphone but didn't pay the last bill?

I bought my brother a iphone 3g and he's giving me his 4gs (it's cracked like hell but i can get an easy 50 bucks for it) to sell on ebay. The reason my brother is giving me this phone is because his bill is like 200 bucks (sprint of course) and he doesn't have the money to pay it so he's letting it shut off. So if i sell this unpaid phone what will happen? Will Sprint confiscated the phone from the person who buys it?

No, you will just still be responsible for paying for it.

Same thing for anything you buy. In this case, you signed a contract in which you agreed to pay for the phone. Getting rid of it or stopping using it doesn't mean you don't have to pay it off.

If you buy a car, you get a loan for, say, $20, 000. Let's say I'm tired of it after 1 year, I still have to pay the loan off. I can sell the car and us that money to pay off the loan but I'm still responsible to pay off the loan.

It will become a bad esn and the phone will become useless.