gContactSync now synchronizes e-mail address types and screenname protocols from Google and shows them in the Thunderbird Edit Card dialog. The types and protocols are chosen through a drop-down menu. Valid e-mail types include other, home, and work and valid protocols include Google Talk, AIM, ICQ, MSN (Windows Live Messenger), Yahoo (Messenger), and Jabber.
Google also allows different types of postal addresses and numbers, but I do not plan to implement those at this time. If you would like me to, however, let me know.
They, like all other added attributes, are not present in the New Card dialog. Before the first patch for Mailnews Bug 413260 landed, it was impossible to add custom attributes to an address book card without first adding the card to an address book and then modifying it. It has landed, but is only on the last few trunk nightlies, so, for now, no custom attributes will appear on the new card dialog. I give some additional information in my response to gContactSync bug 19753.
This feature will appear in the next release soon.
The screenshots are fairly large, so I’ll post links to them.