I have a PC and a Linksys SPA3102.
I have connected them directly with an etthernet cable (pc address 192.168.0.10, linksys address 192.168.0.1). An analog phone device is connected to linksys (plugged into "Phone" socket).
I turned off PC's firewall.
In Linksys configuration I set: Preferred codec: g711a (PCMA) Register: no; Make call without reg: yes; ans call without reg: yes;
I use pjsua (http://www.pjsip.org/pjsua.htm) to make a call call with arguments
pjsua --bound-addr 192.168.0.10 --no-vad --add-codec pcma sip:192.168.0.1
The analog phone rings but when I answer it no sound is available in any direction.