I now have Multiple users in my home with iPhone’s, making standard iTunes syncs suddenly not an easy task! The problem really comes into play with the App Store and iTunes account credentials being stored on the iPhone itself.
These credentials, which require password entry, make it possible for you to download iTunes Applications on your iPhone while not connected to your computer. This account information is entered via the iTunes application, but is not accessible on your iPhone itself. Meaning, once you’ve sync’d and account there is no way to modify the information on the device until you re-sync correctly.
If multiple users are utilizing the same PC or MAC for iPhone, or iPod Touch, it is very easy to store another users iTunes account on your iPhone. This is because the iTunes account which is logged into iTunes at the time of sync is the one in which you iPhone or touch device gets. Seems rather odd right? My Wife and I recently encountered this, initially not sure why each others phones were prompting for the others iTunes accounts.
A quick search on Apple’s Support site turned up the following, confirming the situation:
Products Affected
iTunes, iPhone, iTunes Store, iPod touch, iPhone 3G
Summary
When you sync your iPhone or iPod touch with your computer, the account last used to access the iTunes Store from the computer is synced to the mobile device for use in the iTunes Store from the device as well. This same account is used for the App Store as well. This account will be used on the device for both stores until you sign in from your computer to the iTunes Store with a different account, and then resync your mobile device with the computer.
The solution is really simple, just be sure on sync that you are signed into iTunes via your account. But why would iTunes let you sync, backup, and perform various other functions with an iPhone attached to someone elses iTunes account? This just seems wrong to begin with. Apple, thus iTunes, knows your device does not belong to the other iTunes account. Right?