Do I have to pay for music for my iphone 4?

I already have music on my iTunes. Can I just sync it onto my iphone? Or do I have to buy the music for my phone? So can I sync the music to my iphone like I do with my Ipod Touch?

Yep, as long as you're connected to the same Apple account, there shouldn't be a reason why you can't transfer music to your iPhone.

Just add music to your iphone, the same as you would to your ipod touch.

It's free, don't worry about it.

Once it's in your iTunes library, you can put it on any device that can be synced to that account.