- Go to [Your Name]->Settings.
- Select iCloud from the menu.
- To turn it off, go to Contacts and press it.
- Restart your iPhone if necessary.
- Return to Settings-> [Your Name]->iCloud after that.
- To reactivate it, go to Contacts and press it.
Check your phonebook or contacts list to determine if it's already loaded with all of your contacts information after restarting your iPhone.