http://forums.wireless.att.com/t5/Apple ... -p/1459089

this just helped a ton.

i sync my iPhone to the home PC. i wanted to be able to plug in the iPhone on the work PC and play the tunes on my iPhone through the work itunes; however, it would not let me, and the music was gray and unplayable.

following the steps at this link (ie, copying the ".itl" file from the home computer, and pasting it inside the itunes folder at work) totally worked.

i'm listening to itunes music at work now. woo!

yeah its just like keeping your itunes library on an external HD with all the music

it always frustrated me that i cold do the above with an ipod but not an iphone. not sure what the distinction is...