If I put iPhone music to iTunes, will I lose stuff?

I recently purchased a new macbook pro. I have an iPhone 4, and my iPhone 5 is coming in soon. I need to put the iPhone 4 music to my new laptop. I previously had it hooked up to another computer, my old one. It says that I have no music on my macbook pro, so when I plug in the iPhone 4, I will lose it all and have no music on it.

It is possible to transfer your music to a new computer and new iPhone. Here is a couple of options:

http://support.apple.com/.../kb/HT4527