Well there is one tricky way: It involves modifying your iTunes library xml file on the MBA. You see, the iPhone wont let you sync your music to any computer die to copyright reasons. So you have to trick the iPhone into thinking that the new MBA is actually your original computer. And this is done by the library ID type thing in the xml file. If you want to know how to do this, then just ask and i'll write up a small guide showing how its done. Its quick and simple.
Kris