If you do not have it set to sync automatically, you should manually sync it now.
You can start the sync by pressing the "sync" button that appears in the bottom right corner of the i Phone "Summary" tab in i Tunes.
You still need to restore your settings and sync your data back to the i Phone.
The i Phone will restart automatically; while you're waiting, you can move on to the next step.
After your i Phone restarts, you may see an icon on the phone that indicates it is connected to i Tunes; this will disappear and you'll see a message on the screen saying the i Phone is waiting for activation.
This can take a few minutes, but when it's complete, you will see a message saying the phone has been activated. On the screen, you'll see two options: Set up as a new i Phone and Restore from a backup.
After you've made your selections, hit the "Apply" button that you'll see in the lower right-hand corner of the i Tunes screen.