Are you syncing contacts from your Address Book on your Mac to your iPhone via iCloud or iTunes? If so, check to see if the duplicates are on the computer. You can do that by opening Address Book > Card (menubar) > Look for Duplicates. Afterwards, sync your phone to iTunes or, if you use iCloud, it will sync automatically.

If that is not the case, tell me more about where the contacts are being synced from.

If you have iCloud syncing Contacts, as well as, iTunes syncing your Address Book, that is probably the problem.

1. Open iTunes
2. Select iPad under Devices
3. On the right side, select the Info tab to see if 'Sync Contacts' is selected.

On your iPhone, open Contacts > select Groups > and see which Group you have selected. Sometimes having All Contacts selected can cause duplicates. You can also try the following:

On your iPhone, go to Settings > iCloud > turn off Contacts > select Delete from iPhone > turn Contacts back On. It should sync the correct

If you have All Contacts selected, you could have duplicates because say you have Gmail, your computers, an iCloud account. If all of them have the same address and they weren't merged, then they would show.

To solve this problem, you should just select "All on my iPhone". When you want to view other accounts, you can select that group or select All Contacts.

Do you have Lion on your computer? If so, it has iCloud, and most likely turned on. You should open up Address Book on your Mac and check for duplicates. Address Book > Card (menubar) > Look for Duplicates.

Does that make sense? I know it can get a little confusing.