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While you can sync multiple devices into one iTunes library, for the most part, you can't have one device that syncs with multiple libraries.

If you try to sync a device that's been setup with a different iTunes library (i.e. yours) on another iTunes library (i.e. your wives), you get the prompt that you got.

What in her library were you trying to sync? Some iPhone apps?

Yes.. Since the device was synced on another library you can't. However, you should be able to right click on the device and then transfer purchases. So then all the apps and everything you have on your device will be on the new computer you wish to set up syncing with. Then when you click transfer and it tells you everything will be wiped out it is okay because you will get them back with syncing to the new machine.
 
My wife and I also share 1 iTunes account with two iPhones. I have it set up a bit different though.

Instead of using one account on our mac - we each have our own account (so contacts, calendars, bookmarks are separate). I have our iTunes library with music and apps in the shared directory (you have to make sure you set permisions for all users) and have iTunes set up on both user accounts to use the library in the shared directory. (option click to select).

When I get home later I can type a more detailed post if someone is interested - I am post from my iPhone.

I'd be interested in that information.
Thanks
 
My iphone is synced to my MacBook & my g/friend's iphone is synced to her windows pc. We have separate itunes accounts. Is there any way, if I changed her itunes account to mine, that I could sync her phone on my macbook?

what would happen if I signed her out of itunes on her phone and signed in with my account when I connected her phone to the macbook?

Confusing I know. Thx.
 
I have 2 iPhones and a iTouch on the same account, have a paid app on all 3, but only paid once..all on the same pc too(but i dont know if that matters)
 
iTunes remembers whatever sync settings you setup for each device.

The only manual work you may want to do is setup different groups of contacts in Address Book, a second calendar in iCal, and different playlists in iTunes.

When you plug in the first iPhone, you can tell iTunes to only sync one of the groups in the Address Book, whichever calendar, and whatever playlists for that phone.

You can set the second iPhone up to sync the other group in the Address Book, the other Calendar, and whichever playlists for that.

iTunes will still automatically sync, but only what you've told it sync for that phone.

IMO, it's easier to figure out by playing around than to explain. :)
Don't forget, if you sync to MobileMe, uncheck those in your iTunes device tabs (when your device is plugged in and you click on the device in the left menu and you get those tabs for syncing your device such as Summary, Info, Music, Photos, Books, Podcasts, etc.). If you don't uncheck those items in iTunes and you sync to MobileMe, you will jack up (duplicating some, deleting others) your bookmarks, contacts, etc.

I prefer this method though instead of having two separate user accounts on my Mac and then dragging the iTunes and iPhoto libraries into the "Shared" folders, but YMMV.
 
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