To send and receive messages on GNU/Linux using a TPE-USB4G2US (we've done our testing using the global variant with the EG25-G chipset) USB modem you'll need to install Pidgin and a plug-in for Pidgin called purple-mm-sms. This can be found in most distributions. In most instances you'll already have support for the modem itself via ModemManager, but if this is not installed it will also need to be installed as it is a requirement for using the modem on GNU/Linux.
Note: We believe we've tested this solution already, but failed to document it more thoroughly at the time. If your interested in SMS messaging on GNU/Linux through a graphical utility such as the Pidgin instant messaging client please contact support and let us know your looking for additional documentation on it. We've not yet gotten around to adding this documentation beyond the outline on what is needed to be done here. Please reference this page when sending the inquiry.