We have only one mailing list so far: cordia-dev
This is a very low traffic mailing list, and you can discuss both Cordia HD and Cordia Tab related topics there.
To subscribe, send an e-mail to the firstname.lastname@example.org address. List archive is available at http://dir.gmane.org/gmane.comp.handhelds.cordia.devel
See you at #cordia on Freenode. :)