How to change the computer my iPhone/iPad synch's with??

I hope I've got this post in the right section. I've just switched to Mac and I'm really liking it so far. But, I've been using an iPhone for years and have always synched it to my PC. Now I want to start synching with my Mac (an iMac) but iTunes on the iMac seems to want to re-write my iPhone. When I hook the phone up and start checking things to synch it warns me that my iPhone will be overwritten (yikes!).

Isn't there some way to have my iPhone write everything to iTunes the first time? Or some way to transfer everything from my PC?

All my software is up to date, I'm running the current version of Lion, iTunes, the iPhone iOS, and iTunes is authorized on both computers. I've moved my iTunes music library and don't care about that getting overwritten. But I do care about apps, pictures, text messages, and such.

I take it you've transferred all of your music over from your PC to your Mac?

If so, did you copy over the iTunes Library file with it too?

If not, copy it from your PC (Found in the iTunes folder in My Music), and paste it in your iTunes folder on your mac replacing the original. This should store all your information about your iPhone and what syncs etc (Well, I think so anyway as copying the file over worked perfect for me when connecting my iPhone to my MacBook the first time, nothing was deleted or overwriten).

Hope this helps.

Yes, I have transferred all my music over to the Mac and have since made lots of modifications to the library. I'd rather not overwrite my new Mac library if I don't absolutely have to. I looked at the library.xml file on my pc with notepad. It looks like it's all just HTML formatted text and only seems to have information on the music library. I don't see anything pertaining to the phone. Are you sure this file contains phone data?

Another new Mac user here, but I might be able to help. Have you de-authorized iTunes on your PC and authorized it on you Mac? I found nice instructions on how to cleanly move your entire iTunes library over to the Mac from a PC, followed those and it moved clean as a whistle. After de-authorizing on the PC and authorizing on the Mac, plugged in my iPad and iPhone and both just acted like they'd been syncing with my Mac all the time.

Ok, I figured out how to do it, here's the process:

First, this is how to transfer the ability to synch your iPhone from one computer to another without erasing your iPhone in the process. It will move over things such as apps and all the data in the apps (game progress, passwords, pictures, documents, etc). I use Pocket Informant for my calendar and it preserved all of that data. It also preserved my 3 stars on on levels status in Angry Birds. ;-) It will preserve each page and location of all the apps, folders, etc. It will also preserve settings such as wi-fi networks and email accounts. I believe it preserves everything that is preserved whenever you do a backup. I did loose custom ringtones, not sure why, but so far that's all I can tell I've lost. Not a big deal. Also, I was already synching contacts, bookmarks, and such over iCloud, so I didn't even try to get that stuff to synch. And I didn't try to get the iTunes music library to synch, or podcasts or movies. I was already moving my iTunes Library using other write-ups and I'd guess that is the best way to move it. FYI, the iTunes Library file is only music, it has nothing to do with apps and such, so moving that isn't enough.

I was going from a PC to an iMac and I have an iPhone 4s, but I think this would work for transferring the synch ability from any iTunes on any computer to another. Before you do this, backup everything you can in case something goes wrong. Be sure to do a backup (not just synch) to your current iTunes computer.

So here's the process, this is all done on the new iTunes you want to synch to:

1. In iTunes, get the latest software, authorize the new computer, and download all your previously purchased apps, music, etc.

2. Open the new iTunes, go into Preferences then Devices and select "Prevent iPhones, iPods, and iPads from synching automatically." You DO NOT want to synch when you first hookup your iPhone.

3. Now, hook up your iPhone. When it appears in iTunes under Devices right click and select Backup. You should also be able to backup with iCloud just the same, but I didn't do it that way. Once this finishes you can now backup and restore from this computer.

4. Now go through the menus at the top of iTunes and select all the stuff you want to synch, apps, photos, and such. But not stuff you synch over iCloud. You'll get a message that your iPhone will be erased and it will, click Ok or Proceed or whatever.

5. Now synch your iPhone. It might take a while and when this is done a bunch of stuff will have been erased.

6. Next go back to the left side of iTunes, right click on your iPhone and select "Restore from Backup..." This will take a while too, it will load everything right back onto your iPhone just the way it was before.

7. Last step, do another synch. This time, it won't erase everything as your iPhone is no longer new to this iTunes. Check everything thing over on your iPhone and it should all be back to normal. Now you are synching on the new computer.

If you ran into problems or if this didn't work, you should be able to go to your old iTunes and restore from backup to get your iPhone back to normal.