http://wiki.freeswitch.org/wiki/XML_User_Directory_Guide#Groups
http://wiki.freeswitch.org/wiki/Mod_commands#group_call
 
And this intercept example from the default.xml dialplan file:
    <extension name="group-intercept">
      <condition field="destination_number" expression="^\*8$">
    <action application="answer"/>
    <action application="intercept" data="${hash(select/${domain_name}-last_dial/${callgroup})}"/>
    <action application="sleep" data="2000"/>
      </condition>
    </extension>

Note: groups in the dialplan and directory are not related to the mod_limit group insert/delete/call stuff.
-MC