Interface Asterisk with BP250 PABX


We’re looking to change over one of our remote sites from their current PABX over to an Asterisk VoIP solution. The setup will be basically this:

<Remote Site w/ Asterisk server>
-DSL link-


The plan is to put an TDM400P w/ quad FXO ports into the remote server for handling external calls.
BUT we need to be able to interface the head-office side of things with the BP250 based phone system currently in place.

So far we’ve come to the thought of just placing another Asterisk system here and trunking the two using IAX2 and linking the second to our PABX…what hardware would we use to make this happen most effectively? An FXS card?

Kind regards,