I have upgraded every year with a new phone and it just takes a few calls and being calm and polite with the reps. This is what works for me.One the stores in my area are black and white. no upgrade window no new phone. They have told me time and time again the CS reps have more power for upgrades.
1.example of how I upgrade to the DX after only a few months on a bb.
Call customer service have them look up my account and I told them I wanted to upgrade to the dx. They stated I wasn't in an upgrade period. With a few pauses and sighs acting surprised I state all i wanted to do was upgrade to the dx and I know that will restart me 2 year contract. After looking at my family account with 2 lines they said hold on. Pause came back from holding and sure sir we can do that for you today you will have to pay the price of 200.00 you know that? Yes that would be fine and I bought the phone.
I did this with getting my bb too. It's a matter a few calls with the bb hitting the right rep sometimes. Being nice is all it takes.