• after you’ve enabled iCloud Calendar syncing, be sure to have the complete URL that looks like https://p01-caldav.icloud.com:443/123456789/principal in your iPhone’s copy-paste-memory (if you haven’t, go back to the “Advanced Settings” of your iCloud Calendar account and copy the complete Account URL)
• now do as you did for your iCloud Calendar, but this time you should create a new CARDDAV account :
• Settings>Mail, Contacts,Calendars>Add Account>Other>Add CardDAV Account
  • “Server” is contacts.icloud.com [ if that doesn’t work try : carddav.icloud.com ]
  • “User Name” is your iCloud username ( like joe@me.com )
  • “Password” is your iCloud password
  • “Description” is whatever you want to call this account (e.g. “iCloud Contacts”)
  • Go ahead and click “Next” and the CardDAV account wil be set up BUT IT WON’T WORK yet…
  • Go Settings>Mail, Contacts, Calendars> and click the name of the account you just created to open the settings so we can do one more edit.
  • Click “Advanced Settings”, and delete the complete Account URL, then paste the URL that is still in your iPhone’s copy-paste-memory there, but this time you have to adjust it :
  • in the pasted URL replace “caldav” by “contacts” [ or “carddav” ] and replace “principal” (the last word of the URL) by “carddavhome”
  • the URL should now be something like https://p01-carddav.icloud.com:443/123456789/carddavhome

• in “Settings” -> “Mail, Contacts, Calendars”, scroll down completely (even though it might look like a static page and there’s no indication what-so-ever that you can scroll below “Add Account…”)
• in the “Contacts” section, at “Default Account”, choose “iCloud Contacts”
• in the “Calendars” section, at “Default Calendar” (the setting option completely at the bottom), choose your most frequently used calendar as your default calendar

Done !

NOTE : it’s good to know that iCloud-syncing to the iPhone 3G is slightly delayed :

• Address Book / Contacts sync has a delay of up to one minute
• iCal / Calendar sync seems to completely wipe  your calendars clean, while showing a ‘sync spinner’-icon top-right, and then all calendars reappear within one minute

—— UPDATE —–

the above should work, but if you still encounter problems, try these :

– use your @me.com account name (not the old @mac.com)

– if your server address line keeps reverting back to the same pXX-contacts.icloud.com server-URL but doesn’t load any contacts, create a new account using the server-URL it always reverts to (so just “pXX-contacts.icloud.com” without any addition, and with that exact pXX-severnumber you keep getting)

– upgrade to iOS 4.2.1 if you have an older version of iOS (if you can’t upgrade because you have a jailbroken iPhone, try skipping the contacts-syncing instructions after BUT IT DON’T WORK YET… so, just try without…)

– make sure the contacts you are adding on your Mac are added to your ‘iCloud’ group and not an ‘On My Mac’ or other non iCloud group (you can do this by checking in groups), non iCloud contacts will not sync.

– try unchecking contacts syncing in the iCloud settings, restarting your device and then re-enabling contact settings

– don’t bother about messages saying your password is incorrect, just go ahead and test

– make sure that the server-URL you have set is HTTPS not normal HTTP

– check your pXX server number in the settings that are working for iCal-syncing, and then try these URLs :
pXX-contacts.icloud.com
pXX-carddav.icloud.com
pXX-contacts.icloud.com/[contact group]
pXX-carddav.icloud.com/[contact group]

– be patient, very patient on your first sync ; if you have a lot of contacts or calendars, your first sync can take hours and hours… (actually a whole night…)

– if you just want a one-time transfer of your contacts to your iPhone, you can export your contacts as a vCard from iCloud, and eMail them to your iPhone… where you can import them

[ let’s not forget : a special thanks to all who have contributed ! ]