As it was mentioned above... the iTunes sync will create a backup of your iPhone 4. As well, iCloud (if you're using it) does the same thing. When you get your iPhone 5 home and connect it to iTunes... it will prompt you and ask if you want to set it up as "New device," "From a Backup" or "From an iCloud Backup." As long as you have a backup via iTunes sync or iCloud you'll be good to go in moving all your stuff from the 4 to your new 5.