SmarterContacts – Better contact information
by eliminating duplicates in the iPhone address book
Have you lost trust in the data in your iPhone Address Book? Let SmarterContacts help you to clean up!
SmarterContacts helps you find and eliminate duplicate entries in your iPhone Address Book. It uses sophisticated string comparison algorithms to identify contacts with a similar name and allows you to quickly identify duplicate entries. After starting SmarterContacts, the app analyzes your contacts, looks for matching contacts and classifies them according to how similar another contact is:

Based on this information, you can then edit or delete your contacts using the standard Contacts App.
After tapping the button at the bottom of the screen, a list of duplicate candidates is shown:

This list uses the same colors as the main screen, i.e. red for exact matches, orange for close matches, yellow for wider matches and green for no matches.
After tapping a contact, a new view shows the contact and all potential matching contacts:
You can find some more information in the SmarterContacts FAQ.