[Serusers] SER Running but .......

Hi, I already have SER running on my PC but I couldn't go further to establish a communication between two sip phones (softphones on my system). I tried using EKIGA softphone and LINPHONE in UBUNTU but futile. Questions: 1. Can I use SER without specifying "LISTEN=XX.XX.XX.XX" because it was not included in the ser.cfg file which i recently downloaded? 2. Do I need to get NAT transversal inplace before communication can be established despite the use of 2 softphone on my PC? 3. I did the required modification to ser.cfg in order to use Mediaproxy but I keep getting "1 error" each time I restart SER. The modification made was this: modparam("mediaproxy", "mediaproxy-socket", "/var/run/mediaproxy.sock") changed to modparam("mediaproxy", "mediaproxy-select", "/var/run/proxydispatcher.sock") KINDLY HELP OUT. MIKE