ECSTech

I installed ExpressTalk Business Edition on 2 PCs. I registered the phones to my Trixbox (used to be Asterisk @ Home) Server and tried the Intercom Feature. When I press and hold the Intercom button the extension I tried to talk to rings. If I try to answer the ringing a call is established but no audio is heard. Is this a configuration issue with Trixbox? Has anyone else experienced this? Thanks.