Could a Verizon Wireless rep (or just a customer) answer this for me?

Okay, so over a year ago my family's account got "frozen" for an outstanding bill (my sister made it SKYROCKET). We've finally paid it off and my Stepfather just got a Razr with Verizon to "build up trust" again. Now, I have AT&T right now, but find Verizon to be an all around better company. I understand that I need to pay the $200 cancellation fee with AT&T, and I still want to go to verizon. My old verizon phone, an SCH-A850, is pretty obsolete. Would I be able to go back and get a better phone and have the credits toward that phone? Or would I have to pay full price on it. I was thinking about getting an EnV.