Hello, I installed elastix with TDM400P yesterday, edited sip_nat.conf file for our firewall nat setup, and tested something below: 1. Softphone to PSTN phone (PSTN phone can't hear) 2. Softphone to IP-phone (user report to me they heard noise) 3. IP-phone to IP-phone (work) 4. Softphone to Softphone (work) IP-phone brand is Aztech. Thank !