iPhone's songs greyed out in iTunes

Chris Stegner wrote:
but I should be able to play my music on any of my computers, right?

Not when involves the iphone. By design, the iphone will sync itunes content with ONE computer at a time. Any attempt to sync such content with a second computer will result in ALL itunes content being first erased from your phone & then replaced with the content from the second computer.

What you could do is this:
1. First disable auto sync when an ipod/iphone is connected in itunes, under preferences, which in Windows is under the edit menu.
2. Connect your phone, itunes running, DO NOT SYNC!
3. Go up to Store>Authorize this Computer.
4. Next, File>Transfer Purchases your purchased content will be transferred, music you ripped on your own won't.

You should be able to play your music now.

I've tried all this -- I have two libraries, one Mac & one PC, and the iPhone (3GS) is autosynced in neither. When I use other iPods on this computer (PC), so long as they are set to "manually manage," I don't have any trouble. But with my iPhone, everything is greyed out. If I try to click "manually manage" on the PC, it says that it will delete everything and sync with my PC's iTunes library, which is not what I want.

Any other suggestions?

I can confirm that this does not work. I had an iPod Touch 3rd Gen, and could play music off of it on any computer, and copy 'ripped' music to it from any authorized computer.

I upgraded to an iPhone 4 and now it's over. The music stays greyed out except on the 'home' MacBook, even after the above procedure. There is a page online that tell how to edit HEX files on two computers, but come on! Why does it have to be so hard, Apple?

This is NOT a feature of iphone.

You can sync/manually manage/access music from ONE and ONLY ONE computer at a time. You cannot access the music on your iphone with another computer. You cannot manually manage with two computer. It is not a feature of iphone.