Smssend
SMSSend is a software application for sending SMS messages from an internet connected computer. It is a scriptable application, allowing you to write scripts to send SMS from the application to any web based SMS sending site. There are a large number of scripts available, allowing SMS to be sent worldwide. A lot of the scripts are for free SMS sending services.
The program is available for Windows and Linux, there is a console version for integrating with other scripting languages and a GUI version. The source code for the Linux version is available on the SMSSend website.