Most generous trade-in program – T-Mobile
All four major carriers have trade-in Web sites where you can enter the old phone you have and find out its trade-in value. Time constrictions didn't allow for an in-depth test, so we used a simple one: what would the four carriers give for the BlackBerry Torch 9630?
In the case of the older iPhone, Verizon wouldn't take it, but the other three did. For the iPhone 3GS 16GB: