... of TDM400P.It can be used to build a PBX/Voicemail/Conference system based on Asterisk Open Source platform. Description:1. ... Modules Design: Up to 4 FXS/FXO ports or ... low price.9. Application ready: Use Asterisk, Trixbox, Elastix,Freepbx, etc., more free software to build your IP PBX/Voicemail/ Conference system ...