I manually entered all my contacts and you are saying iTunes saves them?
If you entered a group of contacts into the iPhone directly, then you should sync it next time you plug it in to your computer. Not sure if iTunes saves them itself, but it does transfer them directly from the iPhone to your Contacts (Addressbook with a Mac). It will also sync any contacts you have added directly to your computer, to your iPhone contacts if they are not already there.
Samething works with adding music or videos to the specific playlists you have set up within iTunes.
So, as long as you have "synced" recently between iPhone and computer, you should have a complete backup of everything and your should be able to restore a brand new iPhone to the previous one's state with a one time sync in a couple of minutes.