The CPAN distribution is the latest stable version. Using CPAN means updates can be installed relatively easily.
To download, make and install the script and required modules:
cpan -i WWW::SMS::IE::iesms
Using the SVN version means you have the latest version of the software. This is useful if a fix has been checked in, but a release has not been pushed to CPAN and Debian yet.
Use the Dashboard Widget or build and install the command line version as above.