I recently purchased a MacBookPro which I synced to the same iCloud account that my iPhone is synced with. When I did this, the birthdays of all my contacts showed up as a day late on my MacBookPro. So I decided to resync them.
I (incorrectly) went to the preferences for the Contacts app on my MacBookPro and changed the account to "On My Mac" and then deleted all of my contacts. Then my brain caught up and I quickly went to System Preferences and stopped iCloud syncing contacts. Too late. Now my iPhone has no contacts either. I don't suppose there's any way of getting them back?