How do I change the computer that is synced with my iPhone without erasing fileson either devise?

Every time I try to change the computer, that I first registered my iPhone to, it says that I will lose all the files that I have purchased. Now I think that is stupid and I am not going to re-purchase everything. Especially when I was under the undestanding that the iPhone was portable between computers.How do I change the computer that is synced with my iPhone without erasing fileson either devise?
In response to Sam, that is only true about applications. If you are talking about music, first make sure both computer are authorized for your itunes acct(under the store menu) and then when you plug the phone into the second computer, do not sync. Instead go to the file menu and go to transferr purchases. this will take care of any songs you have purchased for the itunes store. applications will also be transferred over. photos not taken on the iphone cannot be transferred. if any applications get lost, you can redownload those for free as previously mentioned.How do I change the computer that is synced with my iPhone without erasing fileson either devise?
Noooooo, do not re-purchase! lol if you are jailbroken, there is a small software that you can add and install into the iPhone that will allow you to sync with multiple computers... Swaptunes :) simple to use, and works well....
You would have to have an external flash drive and drag and drop all your songs and photos and videos from your old computer into it and it has to have enough memory (Of course :^P), and put all of your data from that flash drive into the current computer you are using. NO JAILBREAKING REQUIRED!!!!!!





Hope this helps! :)
If you purchased the content through iTunes, all you have to do is have iTunes on the new computer and then sign in to the iTunes store and click to download the content again. It will give a message saying that you already purchased that content and will let you download it for free.