Hooray, Finally I can sync my address book 5 (osx snow leopard) with iCloud Full Instruction: http://www.hsiaoi.com/blog/?p=512 1. Create an Account in Address Book 5 with CardDav Setting Username: firstname.lastname@example.org Password: password Server: pxx-contacts.iclould.com It doesnt really matter what you entered, we are going to change from Configuration.plist 2. Close Address (Apple Key + Q) 3. Open Terminal 4. cd Library/Application\ Support/AddressBook/Sources 5. ls -l (search for the latest updated directory) 6. cd [the directory name] 7. nano Configuration.plist 8. Ctrl + W (Search) servername 9. Change the servername <string> by entering this format <string>https://pxx-contacts.icloud.com:443/xxxx your icloud id xxxxxx/principal </string> 10.Change username <string> <string>username%40xxxx.comassword</string> 11. Ctrl + X and Save 12. Open Address Book, iCloud should be Syncing!