The Skype version for Linux is still lagging behind in terms of features compared to the Windows and Mac versions. One feature which most people miss is the ability to send text messages. For me it is quite puzzling how a company is not implementing features which would help them to earn more money (they charge you for sending text messages). However I discovered an alternative, today. It is called skysentials and works pretty well so far.

The way it works is simple. You start Skype first. Then you start skysentials which attaches itself to Skype and accesses user account information like your contact list. In the end you just enter the target mobile number and message text. Get it here. You might also want to have a look at this forum topic which offers advice regarding the installation and potential bugs