Well, you can actually do that. This is part of the technology of SyncML that was enabled by Google for quite some time now.
"Settings > Connectivity > Data Transfer > Sync > Options > New sync profile"
"Contacts > Options > Synchronisation > Settings > Create New"
to start the wizard.
- Page 1/10: Profile Name
Any name that floats your boat.
- Page 2/10: Server Version
- Page 3/10: Applications in sync
check only "Contacts" option
- Page 4/10: Contacts Database
"contacts". Must be all lowercase!
- Page 5/10: Data bearer
- Page 6/10: Host address
- Page 7/10: Server ID
- Page 8/10: Username "your gmail address that includes the @gmail.com"
- Page 9/10: Password "your gmail access password"
- Page 10/10: Activation "Click "Yes" to activate profile"
goto "Contacts > Options > Synchronisation > Start".
Update [26 JAN 2011]:
At the first sync with Google Contacts, some contacts might be duplicated (both phone & Google Contacts). To clean up, on a PC, go to contacts.google.com and hit the Find Duplicates button. It will put them all together so you can click Merge after reviewing them. Now go back to your phone and tell it to sync again. Sometimes you'll need to do this process twice. => Thanks gggirlgeek
Update [12 NOV 2013]:
This method still works according to Carl Boshoff.
Username: username without the @gmail.com part
Password: Generated password from your "Connected applications and sites" passwords