Sorting out Apple ID
All Apple services use Apple IDs: iTunes Store, App Store, Books Store, Game Center, Find MyFriends, Find My iPhone, iMessage, FaceTime and iCloud etc.
All purchased items are forever tied to the Apple ID used to purchase.
In a family, you can configure iTunes Store, App Store and Books Store to use the same purchasing Apple ID.
With that, one can share the items bought with the family without re-purchasing.
Now for all the other Apple services, you can/should use a different Apple ID
Example: My son and daughter both have iPod Touch, they use my purchasing Apple ID for books, music and apps. But they have their own Apple ID for the other service like FaceTime, Game Center, iCloud and iMessage.
Now they can iMessage/Face Time me and their friends.
Unfortunately - the original question wasn't answered. I have the same question. To clarify, I have a wife and kids who each have their own apple devices and their own apple id's. I now want to update all the devices to use the same apple id for purchases only so we can all pay once for the same music.
If I have a device that already had songs and apps purchased on it can I change the iTunes apple id on it and it keep the songs and apps already on there? i'm not syncing to a PC or Mac. I just want to make sure it won't wipe the device. I'm guessing not but want to confirm.
Purchases are linked to Apple IDs. If you change the Apple ID that's one thing, but if you create a brand new Apple ID you will not have access to any purchased content that is linked to another Apple ID. You won't "lose" the content, technically, but you'll have to pay to download the songs again with the other Apple ID.
Changing the Apple ID actually means you change the email addresss. Say, from @yahoo.com to @hotmail.com. You are NOT creating a new Apple ID, but are just changing your Apple ID by using a different email address.