Problem with Preordering

I'll just say this first, I have an old 2007 blackberry that still is running on tmobile and my final goal is to get an iphone 4s 16gb running on my tmobile plan for the unsubsidized price of $649 without tax.

My initial thought was to just preorder an unlocked version form day one but i have heard of other members saying that apple usually doesn't release unlocked phones until much later.

So if they sell the unsubsidized versions on day one I will buy. But what other ways can i achieve my goal. Can i just sign up for 2 years and cancel on day 31? Are there other fees than the EarlyTermFee that will surpass the $649? Will this harm my credit or should i use cash?

Thanks for the help.

 

I totally understand, my current tmobile plan doesn't have any 3g data. Everywhere i go, home, university, work, has wifi so i'll be fine.