trade in trade up service not working, useless

the trade up trade in service is useless, existing cellc customers can't use it, only for upgrade or new lines, which doesn't makes sense as you will get a new phone when you upgrade or get a new phone usually with a new line/number. So what is the point of this service? I can understand if you hand in your old phone lying around, but what about your current phone to trade up? As I understand it and how a customer care agent explained it to me is that existing clients can upgrade their existing contract phones to a better or newer phone. so what is it suppose to be? I get 2 different explanations, which doesn't get me anywhere.