TextNow - TextNow is a mobile virtual network operator (MVNO) that provides a free phone service to users by using other cellular networks coverage.
Empathy - Apps/Empathy - GNOME Wiki!
Google Voice - Google Voice gives you one number for all your phones, voicemail organized in an email format, free...
Gajim - Full featured and easy to use Jabber client
RingCentral - RingCentral is the leading provider of cloud-based communications and collaboration solutions for small business and enterprise companies
IM+ - Chat everywhere! IM+ is the most widely used mobile IM app! Connect all-in-one to MSN, Yahoo!, Goo...