For production environments (call centers, daily business use), use or a hardware SIP phone. For occasional VoIP or testing, MicroSIP via Wine works surprisingly well.
Microsip requires a few dependencies to be installed on your system. The required packages are: How To Install Microsip On Linux
wine ~/Downloads/MicroSIP-x86-setup.exe
MicroSIP is light, but Wine adds overhead. To minimize: For production environments (call centers
sudo dpkg --add-architecture i386 sudo apt update sudo apt install wine wine32 wine64 daily business use)