Linux.com: Four Linux Softphones Reviewed

“Many businesses are turning to Voice over IP (VoIP) to save
money on infrastructure and communications costs, but just ripping
out your existing phone system and replacing it with VoIP will not
work. VoIP systems require IP phones or analog telephone adapters
to allow your existing phones to work. If equipment costs are
stopping you from experimenting with VoIP, softphones can provide
an inexpensive way for businesses to get up and running with VoIP,
as I recently discovered by putting Kiax, Linphone, Twinkle, and
CounterPath’s X-Lite to the test…”