Install sipwitch by entering the following commands in the terminal:
sudo apt update sudo apt install sipwitch
Description:
secure peer-to-peer VoIP server for the SIP protocol
GNU SIP Witch is a secure peer-to-peer VoIP server. Calls can be made even behind NAT firewalls, and without needing a service provider. SIP Witch can be used on the desktop to create bottom-up secure calling networks as a free software alternative to Skype. SIP Witch can also be used as a stand-alone SIP-based office telephone server, or to create secure VoIP networks for an existing IP-PBX such as Asterisk, FreeSWITCH, or Yate. . This package contains the sipwitch daemon and related utilities.
Homepage: http://www.gnu.org/software/sipwitch/
Version: 1.9.15-3
Section: universe/net