[Asterisk-Users] Meetme conference across WAN

[pashah]

Greetings,

I have 4 asterisk boxes in 4 different locations,
works perfect [over ip with ipsec + asteriskes use IAX 
to talk to each other]. 
Users can call each other and talk no problem,
sound quality is fine.

asterisk is great.

I am to create the conferencing facility.
and I am stuck.

The TDM400P card is installed in one of the asterisk boxes [zaptel,
wcfxs and crc_ccitt modules installed ok],
Users in that location can create and connect to conferences
on that server.

the question is:

Could anyone point me to some documentation [or share conf files]
which will describe what I am to do in order to connect user from
different location to the conference
created on that asterisk box with TDM400P?

thanks in advance.
-- 
pashah