Two iPhones with one iTunes

Apple iPhone - Two iPhones with one iTunes

I have 2 iPhones, mine and my GF's. I would like to sync music etc on hers and contacts, apps on mine. Is it possible to set what syncs for each iPhone depending on which one is plugged in. Another words would iTunes know that I am plugging mine, therefore, sync: contacts, pictures, music, apps, books. If hers plugged in; sync: apps, music, photos. Is this possible.

iPhone iTunes
Yup, each device uses the 40 character UDID to identify it - you can plug as many iPhones, iPods, or iPads you want and iTunes reads from the device what to sync - backups will be stored in the computer (location depends on OS) in /User/Library/MobileSync/iTunes/40charactername/ or \Users\User\AppData\iTunes\MobileSync\40charactername\

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I'm up to six devices of various types & vintages with no problems.

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Same. No problem here with 2 iPads, 2 iPhone, 4 iPod Touch. From old to new.

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Of course. Each iPhone (or iPod, or iPad) is recognised as a different device by iTunes. Each one has its own preferences and settings.

If you had your own users on the computer, you would each have your own iTunes. I assume you share a user?