Many iPhone users has start to lose their contacts when they change to Backup on iCloud during their upgrade to iOS 6 software. Our Android friends do not face this issue as their Contacts are store on the Google(Gmail) Account.
I will share with you on how some iPhone users has overcome this:
- Connect iPhone to iTunes
- Go to iPhone Summary
- Unclick the Back up iCloud
- Click the Back up to computer
- Go to info tab, at the bottom(advance settings)"Replace info on this iPhone"
- Click on Contacts
Do not depend on iCloud too much. Ensure that you backup to your computer quarterly to avoid any contacts missing.