I tried HTC Sync, and had some issues, so switched to CompanionLink. For me, the synchronization between HTC contacts and the Google online contacts was causing a problem: contacts (generally those with categories) are removed from the phone and moved to the online contacts. Here is how to fix that. First, if you have used HTC Sync, you must clear out all the data it put into contacts and into calendar. Do that as follows: Settings | Applications | Manage Applications | Calendar Storage | Clear Data and Settings | Applications | Manage Applications | Contacts Storage | Clear Data If you have attempted to use CompanionLink before doing the above step, you should also go to the SD card and use a file manager to delete the clusb directory on the SD card if it exists. That clears CompanionLink data and you can make a fresh start. Next, disable Google Contacts sync on the phone as follows. On Settings | Accounts & Sync: check Background data; check Auto-sync; then hit Google. Uncheck Sync Contacts (and Sync Calendar if you don't want that to sync). Hit the back key to return to the previous screen. Uncheck Auto-sync if desired.