My phone's screen is broken, and I can't afford a new one. My service plan isn't up for another year. I called Sprint, and the customer support rep said they wouldn't allow me to add the T-Mobile phone that my sister gave me. The hardware seems to be almost exactly the same, so I don't understand why I can't use it.

probably not cuz t mobile runs on different band lengths.. verizon phones work with spring i doubt if t mobile phones do.. sign a new contract with sprint they'll give u a free phone..