Ok I just talked to my local Apple store in Michigan and he verified you do NOT need your current phone with you (After I verified AGAIN that they still had my reservation. Yes Im paranoid).
And for users like myself who are selling their current iphone first just remove the SIM from the phone and it basically deactivates it. Then when you get the new one it will be activated on the spot as it has its own SIM and is actually a different size than the 3GS/3G sim.