If you start with a clean slate (one way sync either to yahoo or to the device) the 2way sync works perfectly when you add a new contact or update one. If you happen to add the same contact to both yahoo and BB you may end up with a duplicate, but that defeats the purpose of syncing. Just add it once in one place and sync.
Let me be more clear...I converted my wife over from a "dumb" phone to a BB and then some time after that converted her from Gmail to Yahoo. Her Gmail contacts were 99% names and email and contained duplicates. Her BB phone book was 99% names and phone numbers and contained dups. I dumped both files into excel and split the name field where applicable and then merged the two files. I sorted on last name and manually merged all data where possible. Then I went thru and actually read each contact to see if it had a dup somewhere else. (like Cuz Bobby and Cousin Bobby and Bobby N.....). Once this was done I uploaded the file to Yahoo's address book. I then used DM to blow away her old address book and replace it with Yahoo's.
From that point forward DM was able to 2way sync with no problems or dups. Once you have a good working copy, it is pretty easy to keep things neat and clean. If you add contacts to your BB...the next time you sync it will be in Yahoo and vice versa. If you happen to add a contact that already exists somewhere on the other end, yes you will get a duplicate, however, that will happen even with Exchange, BES, and Outlook.
Last edited by Serpentine009 : 01-06-2009 at 10:32 AM.