How to put my music onto itunes from iphone?

I have an iphone and it was connected to the itunes on my old laptop computer. My old laptop's hard drive was wiped a few weeks ago and I got a new laptop. One of the first things I did was add itunes onto it. BUT! I tried to sync my iphone to my account and it added the iphone, but my music didn't transfer. When I clicked on the option to do so, it said everything from my phone would be wiped. How do I get all my music onto itunes without wiping the phone? I need to know because I'm hoping to get the iphone 4s for Christmas and I have a ton of music on my phone and I do not want to lose any of it in the process of switching iphones.

Here is a easer way explained…

To start off:
---What you can do is backup everything you need badly in case something goes wrong. Basically the only things you can't get back are your personal settings for things and Notes - as far as I know.

What you will need:
---External storage of some sort. The bigger the better: less trips back and forth.

To make this simple, make folders called Music, Movies, Podcasts, Audiobooks, Applications, and Ringtones. (Whatever you have, make a folder for it to make things easy as pie, so nothing gets all mixed up.)

1) Music, Movies, Podcasts, Audiobooks and Ringtone files can be copied as simple as a drag and drop out of their sections in iTunes, and onto a Flash Drive or Hard Drive. (So long as they're not purchased from iTunes, explained next.) You can now drag those off of the external storage and on to iTunes on your new computer in the places that they go. Music in Music, etc.

2) For Applications, and all content downloaded from the iTunes Store, you need to "authorize your PC" in iTunes under your current account. To do that, just sign in to the iTunes Store on the new computer with the account you always used. It may ask you to authorize that computer now or later, you want to say yes to that when you see it. I forget when it will ask.

3) Just as you dragged and dropped Music, Movies, etc, drag and drop all of your Applications (and other purchased content) onto that external storage. Drag all that to where it goes in to the new iTunes as well.

Pictures, if you have any, can be dragged out of iPhoto or the Pictures folder, and onto external storage. From there just drop them into My Pictures or wherever you'd like on the new computer.

When you connect your iPhone to the new computer, all of your things will be there, somewhere, and you just have to point your iPhone to them. It will wipe your iPhone, inevitably, as you go to a new computer with a new iTunes Library. The only work left is to go through and check what you do and don't want synced to the iPhone when it's connected… Hope this helps