Just a guess but if you could fit 10 iphones in the same size shipping box as the macbook (the shipping box is bigger than the retail box) Then 320,000.
"By reducing our packaging over 40 percent between 2006 and 2009, we ship 50 percent more boxes in each airline shipping container. That saves one 747 flight for every 32,000 units we ship.*"
The only problem with that is air cargo flies by weight, not size. If the plane has a weight limit equal to 10,000 iPhones, FOR EXAMPLE, then it doesn't matter how big the boxes are. However, given the small weight of the iPhones, then yes the box size would allow more to ship.