You could definitely get your phone now. I am full upgrade eligible on 3/16 and I am getting my phone tomorrow. Went in Monday, asked to get it, and the manager said that was fine. $99 and $18 upgrade fee. Had to get funds together or I would have done it right then and there.
When you go in, just be really nice, tell them you know you have an upgrade coming on the 4th and ask if you can get the phone now because you are so excited about it. At one point the saleswoman said I would have to do the $200 upgrade and I said I was more than willing to wait until 3/16. Then they agreed to the new contract price.