Windows users should follow the Step by Step Instruction for Windows.
Other users should follow these steps:
You can also compile and use the program without root permission, but the installation script needs to be run by root.
If you do not have root permission, you can install the program manually: Create spool directories manually and copy the two files smsd and smsd.conf to any directory. Don't forget to enter all spool directories into the config file because the default settings do not match your setup. Then run smsd -c path_to_config_file/smsd.conf. Of course, you need read and write permission to the serial ports where your modems are connected.