Don’t worry too much, you can get those lost numbers back. It’s not lost forever to the ether.
1. Open iTunes on your computer.
2. Plug your iPhone in to your computer using the USB connector cable.
3. Go to “Devices” on the left-side of the iTunes window and click the iPhone tab.
4. Right-click on the iPhone icon in the “Devices” column and select “Restore from Backup”. Select one of the backup versions from the drop-down menu. Click the “Restore” button. This will restore any contacts that you may have deleted since the last time that you synced your iPhone with iTunes.
5. Eject your iPhone. Go to your contact list. Your lost contacts should be restored.
A couple of notes for you to consider for the future:
•It is recommended that you occasionally make separate backups that aren’t the ones that iTunes automatically does when you sync the iPhone. iTunes replaces the previous backup each time it syncs. To ensure that you keep things that you want or as a just in case, it’s good to have different back ups. Create a separate backup by right-clicking on the iPhone under the “Devices” tab in the left column. Then select “Back Up”. You can also restore contacts manually if you sync contacts with your contact list in either Outlook or Address Book (Mac) and re-entering the info by hand.
•If you haven’t synced in a while you might have to re-download any firmware updates or apps that you have added to the iPhone since the last backup. They won’t be kept in the previous backup file.