How Do I Sync My iPhone, iPad, or iPod touch with a New Computer Without Wiping Out All My Data? [Ask Lifehacker]

How Do I Sync My iPhone, iPad, or iPod touch with a New Computer Without Wiping Out All My Data? [Ask Lifehacker]:

Dear Lifehacker,
I've been syncing my iPhone with laptop, but now I want to start syncing with my desktop. When I connect it to the desktop, iTunes wants to erase everything in order to start syncing with his new machine. I want to start syncing with the new machine, not remove all the content already on my phone. What can I do? More »