What's the deal with people asking simple questions like this lately? Information like this can easily be found on the web or in the iPhone manual. When you sync your iPhone to your computer, it automatically makes a backup of all your settings and installed apps and data. The only thing it doesn't back up are the applications themselves, videos, music and synced photos. What it does back up is, settings, app settings, app data, call data, sms messages, voicemail messages, mail messages, springboard icon layout, address book and everything else that's in your "mobile" user folder. As long as you have all of your apps on your computer and your music on your computer, you should be all set. If by any chance you don't have your apps copied to iTunes, you can right click on your iPhone in iTunes and choose "Transfer Purchases" from the pop-up menu. This will transfer app store apps and purchased music from iTunes, but it will not transfer other music.