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
• Sync

Do not depend on iCloud too much. Ensure that you backup to your computer quarterly to avoid any contacts missing.