Just my opinion, based only on my gut feeling, but I think McCown will start on day 1, and get the majority of the snaps thorughout the season. Beck will be the #1 replacement for games in which we lead (?) or trail by a lot, and Henne will only be played if Beck is having a bad game.
I understand, from Raiders' fans, that McCown is a tough competitor, and that many Raiders' fan were sorry to see him go. He may not be the most talented QB, but he will balance out any lack of ability with toughness. The Phins on the field will rally around this attitude, and we will find out that the Phins will be the most competitive when McCown is the QB.
Kinda makes you remember Jay Fiedler.
I'd like to see Beck step up into this role, but I will believe it when I see it. I'll also be real happy if that happens.