1) Add "groups" to contacts
2) Behave like Google Contacts Groups:
meaning that there is only one list of contacts, but
any contact can be in any group without duplicating
that contact
3) sync to google contact, with groups
4) with google sync I can sync to my iPhone
1. Its planed for RoundCube 0.4
2. That's the standard way groups in a address books works, I see no resion why it will be different.
3. Check out rosali's google_contacts plugin myroundcube - Project Hosting on Google Code (http://code.google.com/p/myroundcube/)
4. Don't know what you mean.