If you have an iPhone or a Windows Mobile, you can now synchronize Google Calendar events and Gmail events using Google Sync. “Once you set up Sync on your phone, it will automatically begin synchronizing your address book and calendar in the background, over-the-air, so you can attend to other tasks. Sync uses push technology so any changes or additions to your calendar or contacts are reflected on your device in minutes,” explains Google Mobile Blog.
Google mentions that the service available for iPhone and Windows Mobile uses the Microsoft Exchange ActiveSync protocol. “When setting up a new Exchange ActiveSync account on your phone, all existing Contacts and Calendar events may be removed. Please make sure to back up any important data before you set up Google Sync.”
Before giving it a shot you might want to Merge Duplicate Contacts using the built-in contact merge feature in Google Contacts. Just find the duplicate contacts, tick their checkboxes, and click “Merge these contacts”.