Sounds like your contacts are out of sync with Handcent & your other accounts. Most times, duplicates arise b/c the backup isn't current or you have contacts stored on SIM as well as backed up by your Google account online? If so, export them to your Google account to back them up and then delete them from the sim card. Sometimes, you can just resync and merge them from accounts & sync. Or just clear contacts storage in settings>manage applications and then resync them. One of them should do the trick for you.