No there is a seperate bridge for that,
you can manually add 6 parties to a call off a G3, thats it
You cannot do a 'dial-into' function.
In the new multivantage (R11) they changed it a little, and you can set it to do , what they call a "meet me conference".
see the avaya site, multivantage bit for details.
Again this is limited to the small numbers of attendees..