Empathy - Apps/Empathy - GNOME Wiki!
TextNow - TextNow is a mobile virtual network operator (MVNO) that provides a free phone service to users by using other cellular networks coverage.
IM+ - Chat everywhere! IM+ is the most widely used mobile IM app! Connect all-in-one to MSN, Yahoo!, Goo...
Talk360 - Talk360 is a best-in-class communication utility that offers a convenient way to connect with loved ones globally.
Pinger - Pinger lets you text and talk free with the people you care about most, anywhere on the planet.
TextMe - TextMe is a free calls and messaging application at both local and international levels.