Default SIP Problems

I'm using ICS 4.04 CM9 TeamChopsticks Alpha 4.
http://forum.xda-developers.com/show....php?t=1621678

I'm trying to connect my phone to my voip.ms SIP account. I'm having some issues though. When I try to make a call it rings but then when the other person picks up it's just silence. I can't hear them and they can't hear me. Is there some configuration I've done wrong? Is this a limitation of this ROM? When I use my Cisco desk phone everything works fine. I'm on the same wifi network as that phone.