DupeDeDupe is a Windows Mobile application which has a basic GUI which allows you to scan for duplicates, and then choose (after being told your duplicate count) whether to remove them.
Contacts are compared based on

File As ,
Email and
Home / Work / Mobile phone

If all those fields match, it’s deemed a duplicate.

Source : modaco.com
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DupeDeDupe

Tags: cell phone, DupeDeDupe, duplicate contacts, freeware, Mobile, PDA, Pocket PC, PocketPC, PPC, Windows Mobile