Syncing on new PC and I now have a new iPhone, help!!

Question

Hi All,
The issue I have is that the iPhone 3GS I use at the moment was first synced on an old PC.  That PC died and I have been syncing to a new PC.  However, when connect to iTunes, it will keep a copy of any new Apps and updates. It will also update the iSO software. However, If I click on my phone (listed on the left side of the iTunes screen and then choose movies or music etc..  The sync option brings up a window saying that the phone was not synced to this PC. to do so will remove all data from my phone. 
Is there anything I can do?  I still have the old hard drive that I could link to my new PC and get off any itunes files?  Will that help? 
The other issue I have is that I have just upgraded my phone contract as was able to get a new iPhone 4s .  I want to give my old 3gs to my wife.  Is it as simple as taking out my old sim card and putting hers in?   Also, how will itune behave if I not have two iphones syncing to the same PC?
Sorry for the odd questions.  But I'm sure you lovely people can help. 
Thanks

Answer 1

Syncing to a new iTunes library or computer will erase your phone. Only if you back up manually before syncing, you can restore your device from that backup again. A manual backup does not include the sync process.
Do this:
Disable autosync in iTunes, connect your phone to your new computer and right click on it in the device list and choose backup. iTunes will backup your device without syncing.
Transfer your purchases the same way, choosing "transfer purchases" this time.
When you connect your phone for the first time, all media content will be erased. But you can restore your settings and app data from your manual backup afterwards.
Don't forget to set up at least one contact and event on your new computer to be able to merge calendars and contacts when you sync the iPhone for the first time.
Music is one way only, from the computer to your device, unless you bought the songs in itunes and transferred your purchases.
There is 3rd party software out there, but not supported by Apple, see this thread:http://discussions.apple.com/thread.jspa?threadID=2013615&tstart=0
About backups and what's saved:iTunes: About iOS backups
How to back up and restore:http://support.apple.com/kb/HT1414
How to download apps for free again:http://support.apple.com/kb/HT2519
Saving other data is also described here. How to back up your data and set up as a new device
As for the second phone, iTunes will recognize each device as a separate phones and remember all settings for each one.
Switching the SIM will work if your phone is not locked to a provider anymore and your wife has a dataplan as well. If the phone is officially unlocked by your provider, she can use it with her SIM, but make sure to set up a dataplan for the phone, using mobile data without a contract can be very expensive.
To prevent from mixing the contacts and events for each one, you can create a new Windows user.
More info here:
How to use multiple iPods, iPhones with one computer