Why would you buy the Note if you're on Sprint? You can't use it. Your out of pocket would actually be more than 625 because you need to factor in the month of service they're going to charge you. A brand new international Note would cost you about the same as going through all the stuff you're contemplating.
Good point. Although I'm with Sprint I was thinking to add a second account/carrier with at&t just for this phone. I have wanted this phone since it was announced last September. I am not under contract with Sprint, since I always buy my phones off-contract. However, I've been with Sprint for over 10 years, but I've heard no rumblings about this phone coming to Sprint.
My real problem is that I would not be transferring my number, but opening a brand new off-contract account. That means for a while I would have two phone numbers and two phones. However, it's the only way to truly test this phone out in real world conditions for use case in my sphere of living. If I like it as much as I think I will then I would leave Sprint and stay with the Note on at&t. If I don't like it, I can always sell the Note, since it will be paid for, and I won't be under any contract obligation to at&t. At that point I would just keep using my GS2 Epic Touch with Sprint until something else comes along.
The cost for the month of service is going to be there no matter which buying option I decide; unlocked International or direct from At&t.