Setting up conferencing

I hope to have some guidance from experienced users in my first Asterisk use.
I would like to setup an Asterisk system to allow conference calls to be established between 4 different callers, my company plus 3 other companies, using VOIP lines from an ADSL service into each company.

In my company I will use a intercom system and line hybrid interface that will connect into the Asterisk PABX.

In my understanding that interface will connect into an FXS port and the VOIP lines from the ADSL modem will connect to FXO ports. Can you confirm the concept and that I will require 2 VOIP lines to allow conferencing to be activated.


I am not an expert, however you should need 3 total outside lines in order to conference 3 extra people into the system. Also it seems it would be easier if you can activate the VOIP service as a SIP system. Then instead of requireing 3 physical phone lines to plug into an FXO card (which costs money of course) you can use existing internet connections to maintain in essence the same result. You could also get rid of the VOIP ATA as well. Again I am not an expert and don’t know enough about asterisk to tell you how, but hopefully this will bring some more discussion into the matter.