
Ekiga Softphone
Talk to and see people over the Internet
Phone Manager
Receive and send text messages from your mobile phone

Linphone
Linphone is a libre SIP client
Yate VoIP Client
Place phone calls over the Internet

QuteCom
Talk to people over the Internet and send instant messages over multiple protocols
SFLphone
Call and receive calls with SIP or IAX protocols
SFLphone VoIP KDE4 client
Call and receive calls with SIP or IAX protocols

Twinkle
Voice over Internet Protocol (VoIP) SIP Phone

Efax-gtk
GUI front end for the efax fax program

Audio assistant
Linphone audio assistant
Ring
Ring is a secured and distributed communication software.

qTox
Qt 5 based Tox instant messenger for secure communication
Mangler
Voice chat on Ventrilo 3.x servers
Ring VoIP KDE client
Call and receive calls with SIP or RING protocols
Jami
Jami is a secured and distributed communication software
Jitsi
VoIP and Instant Messaging client

GNOME Phone Manager
Receive and send text messages from your mobile phone