Miranda NG - Miranda NG is a successor of a popular multi-protocol instant messaging client for Windows - Miranda IM. Very light on system resources and extremely fast.
Google Voice - Google Voice gives you one number for all your phones, voicemail organized in an email format, free...
IM+ - Chat everywhere! IM+ is the most widely used mobile IM app! Connect all-in-one to MSN, Yahoo!, Goo...
TextMe - TextMe is a free calls and messaging application at both local and international levels.
Gajim - Full featured and easy to use Jabber client
Talkatone - Android App on. Google Play. Stop paying for cell minutes, texts & landlines; Turn your iPad or iPod touch into a phone; Call/Text even in areas with bad cell coverage; Call/Text when travelling without paying for expensive international minutes.