The current SVN has an example export module for vCard that I have written a few days ago. It does not
One could use it as guideline for how to do other exports.
The export code should be placed in export.php.
Currently we have only single card export.
Import is drafted, but noone has committed to developing it. See other thread.
Is very interesting there seems to be XML vCard, hCard and semantic XHTM as option for exports.
One could use XML also as Transfer function between instances of TAB-2.
Automatic server2server transfer between instances of TAB-2 could be initiated with a curl interface via some secret TAB-2 passwords that both instances share. The recently changed list can be used as sync base (as long as one never uses phpmyadmin to mess with contacts).
This seems to be the most promising format sofar:
It allows server queries and updates in XML.