I really like my new iPhone 3G however I came across a small problem that was quite hard to track down and solve, hopefully this guide will help someone else out there having the same frustrating problem - music being greyed out when connected to another computer.

Previously I synced my music, at home, on my desktop computer, using an iPod Classic in "Manually manage music" mode. When I got to work on my second machine, my laptop, I was able to plug this in and have access to my music (for playing, not copying) and able to play over AirTunes.

No such luck with iPhone, the same technique simply doesn't work. At first I thought it was related to the iTunes Store authorized accounts, I made sure both desktop and laptop were authorised, but my music was still greyed out on the secondary machine, doh.

After alot of reading around I discovered that this might actually be a bug with the iPhone/iTunes combo, as it doesn't seem to recognise/remember it's in "manual" mode when you connect to another computer, the trigger that is supposed to allow you to play music on another machine.

After even more reading around I found a technique that works and it's really easy to do. From your main machine (the machine that currently syncs with iPhone) make a copy of both "iTunes Library.itl" and "iTunes Music Library.xml" from you iTunes music directory and overwrite them on your secondary location, viola!